Dynamic path for end effector control

ABSTRACT

A system for performing interactions within a physical environment including a robot base that undergoes movement relative to the environment, a robot arm mounted to the robot base, the robot arm including an end effector mounted thereon and a tracking system that measures a robot base position indicative of a position of the robot base relative to the environment. A control system acquires an indication of an end effector destination, and repeatedly determines a robot base position using signals from the tracking system, calculates an end effector path extending to the end effector destination at least in part using the robot base position, generates robot control signals based on the end effector path and applies the robot control signals to the robot arm to cause the end effector to be moved along the end effector path towards the destination.

BACKGROUND OF THE INVENTION

The present invention relates to systems and methods for performinginteractions within a physical environment, and in one particularexample, to systems and methods for moving an end effector in accordancewith a dynamic end effector path to account for relative movementbetween a robot base and the environment.

DESCRIPTION OF THE PRIOR ART

The reference in this specification to any prior publication (orinformation derived from it), or to any matter which is known, is not,and should not be taken as an acknowledgment or admission or any form ofsuggestion that the prior publication (or information derived from it)or known matter forms part of the common general knowledge in the fieldof endeavour to which this specification relates.

It is known to provide systems in which a robot arm mounted on a movingrobot base is used to perform interactions within a physicalenvironment. For example, WO 2007/076581 describes an automated bricklaying system for constructing a building from a plurality of brickscomprising a robot provided with a brick laying and adhesive applyinghead, a measuring system, and a controller that provides control data tothe robot to lay the bricks at predetermined locations. The measuringsystem measures in real time the position of the head and producesposition data for the controller. The controller produces control dataon the basis of a comparison between the position data and apredetermined or pre-programmed position of the head to lay a brick at apredetermined position for the building under construction. Thecontroller can control the robot to construct the building in a courseby course manner where the bricks are laid sequentially at theirrespective predetermined positions and where a complete course of bricksfor the entire building is laid prior to laying of the brick for thenext course.

The arrangement described in WO 2007/076581 went a long way towardaddressing issues associated with long booms deflecting due to gravity,wind, movement of the end effector, and movement of the boom.Nevertheless, even with the arrangement described in WO 2007/076581,errors in positioning of the end effector could still occur,particularly as the distance from the base of the robot and the endeffector increased.

SUMMARY OF THE PRESENT INVENTION

In one broad form, an aspect of the present invention seeks to provide asystem for performing interactions within a physical environment, thesystem including: a robot base that undergoes movement relative to theenvironment; a robot arm mounted to the robot base, the robot armincluding an end effector mounted thereon; a tracking system thatmeasures a robot base position indicative of a position of the robotbase relative to the environment; and, a control system that: acquiresan indication of an end effector destination; determines a robot baseposition using signals from the tracking system; calculates an endeffector path extending to the end effector destination at least in partusing the robot base position; generates robot control signals based onthe end effector path; applies the robot control signals to the robotarm to cause the end effector to be moved along the end effector pathtowards the destination; and, repeats steps (ii) to (vi) to move the endeffector towards the end effector destination.

In one embodiment the end effector destination is defined relative to anenvironment coordinate system and the control system: calculates atransformed end effector destination by transforming the end effectordestination from the environment coordinate system to the robot basecoordinate system at least in part using the robot base position; and,calculates an end effector path extending to the transformed endeffector destination in the robot base coordinate system.

In one embodiment the end effector destination includes an end effectorpose, the tracking system measures a robot base pose and wherein thecontrol system: determines a current robot base pose using signals fromthe tracking system; and calculates an end effector path based on thecurrent robot base pose.

In one embodiment the control system: determines an end effector poserelative to the robot base coordinate system; determines a current robotbase pose using signals from the tracking system; and, calculates theend effector path using the current robot base pose.

In one embodiment the control system: determines an end effectorposition; and, calculates the end effector path using the end effectorposition.

In one embodiment the control system determines the end effectorposition in a robot base coordinate system using robot arm kinematics.

In one embodiment the robot base moves with a slower dynamic responseand the end effector moves with a faster dynamic response to correct formovement of the robot base away from an expected robot base position.

In one embodiment the robot base is a movable robot base, and the systemincludes a robot base actuator that moves the robot base relative to theenvironment.

In one embodiment the control system: calculates a robot base pathextending from a current robot base position at least in part inaccordance with an end effector destination; generates robot basecontrol signals based on the robot base path; and, applies the robotbase control signals to the robot base actuator to cause the robot baseto be moved along the robot base path.

In one embodiment the robot base path is configured to allow continuousmovement of the robot base along the robot base path in accordance witha defined robot base path velocity profile.

In one embodiment control system: determines a virtual robot baseposition offset from the robot base and defined at least partially inaccordance with an end effector position; and, uses the virtual robotbase position to at least one of: calculate a robot base path; and,generate robot base actuator control signals.

In one embodiment the virtual robot base position is coincident with areference end effector position, the reference end effector positionbeing at least one of: an operative position indicative of a position ofthe end effector when performing an interaction in the environment; apre-operative position indicative of a position of the end effectorprior to commencing an interaction in the environment; and, a defaultposition indicative of a position of the end effector followingperforming an interaction in the environment.

In one embodiment the tracking system measures a target positionindicative of a position of a target mounted on the robot base and thecontrol system determines the virtual robot base position using thetarget position by transforming the target position to the virtual robotbase position.

In one embodiment the control system: acquires an indication of aplurality of end effector destinations; determines a robot base positionat least in part using signals from the tracking system; calculates arobot base path extending from the robot base position in accordancewith the end effector destinations, the robot base path being configuredto allow continuous movement of the robot base along the robot base pathin accordance with a defined robot base path velocity profile; generatesrobot base control signals based on the robot base path; and, appliesthe robot base control signals to the robot base actuator to cause therobot base to be moved along the robot base path in accordance with therobot base path velocity profile.

In one embodiment, at least one of: the robot base path does not includeany discontinuities; and, robot base path velocity profile does notinclude any discontinuous velocity changes.

In one embodiment the control system: defines an interaction window;and, determines the robot base path at least in part using theinteraction window.

In one embodiment the control system: monitors end effector interaction;and, selectively modifies the robot base control signals to cause therobot base to move at a robot base velocity below the robot base pathvelocity profile, depending on results of the monitoring.

In one embodiment the robot base path includes an interaction windowassociated with each end effector destination, and wherein as the robotbase enters an interaction window, the control system: controls therobot arm to commence at least one of: interaction; and, movement of theend effector along an end effector path to the end effector destination;and, monitors interaction by determining if the interaction will becompleted by the time the robot base approaches an exit to aninteraction window; and, progressively reduces the robot base velocityto ensure the interaction is completed by the time the robot basereaches an exit to the interaction window.

In one embodiment the system includes: a first tracking system thatmeasures a robot base position indicative of a position of the robotbase relative to the environment; and, a second tracking system thatmeasures movement of the robot base, and wherein the control system:determines the robot base position at least in part using signals fromthe first tracking system; and, in the event of failure of the firsttracking system: determines a robot base position using signals from thesecond tracking system; and, controls the robot arm to move the endeffector along the end effector path at a reduced end effector speed.

In one embodiment the system includes: a robot base; and, a robot baseactuator that moves the robot base relative to the environment, andwherein the control system uses the robot base position to at leastpartially control the robot base actuator to move the robot base along arobot base path, and wherein in the event of failure of the firsttracking system: determines the robot base position using signals fromthe second tracking system; and, controls the robot base actuator tomove the robot base along the robot base path at a reduced robot basespeed.

In one embodiment the tracking system includes: a tracking baseincluding a tracker head having: a radiation source arranged to send aradiation beam to a target; a base sensor that senses reflectedradiation; head angle sensors that sense an orientation of the head; abase tracking system that: tracks a position of the target; and,controls an orientation of the tracker head to follow the target; atarget including: a target sensor that senses the radiation beam; targetangle sensors that sense an orientation of the head; a target trackingsystem that: tracks a position of the tracking base; and, controls anorientation of the target to follow the tracker head; and, a trackerprocessing system that determines a relative position of the trackerbase and target in accordance with signals from the sensors.

In one embodiment the robot base is static and the environment is movingrelative to the robot base.

In one embodiment the control system generates the robot control signalstaking into account at least one of: an end effector velocity profile;robot dynamics; and, robot kinematics.

In one embodiment the control system includes a computer numericalcontrol system.

In one embodiment the control system at least one of: repeats steps forprocessing cycles of the control system; repeats steps for consecutiveprocessing cycles of the control system; and, repeats steps based on arefresh rate of the tracking system.

In one embodiment the robot base includes a head mounted to a boom.

In one embodiment the boom is attached to a vehicle.

In one embodiment the system is used for at least one of: positioningobjects or material in the environment; retrieving objects or materialfrom the environment; and, modifying objects or material in theenvironment.

In one embodiment the environment is at least one of: a building site; aconstruction site; and, a vehicle.

In one broad form, an aspect of the present invention seeks to provide amethod for performing interactions within a physical environment using asystem including: a robot base that undergoes movement relative to theenvironment; a robot arm mounted to the robot base, the robot armincluding an end effector mounted thereon; and, a tracking system thatmeasures a robot base position indicative of a position of the robotbase relative to the environment and wherein the method includes, in acontrol system: acquiring an indication of an end effector destination;determining a robot base position using signals from the trackingsystem; calculating an end effector path extending to the end effectordestination at least in part using the robot base position; generatingrobot control signals based on the end effector path; applying the robotcontrol signals to the robot arm to cause the end effector to be movedalong the end effector path towards the destination; and, repeatingsteps (ii) to (vi) to move the end effector towards the end effectordestination.

In one broad form, an aspect of the present invention seeks to provide acomputer program product including computer executable code, which whenexecuted by a suitably programmed control system causes the controlsystem to control a system for performing interactions within a physicalenvironment, the system including: a robot base that undergoes movementrelative to the environment; a robot arm mounted to the robot base, therobot arm including an end effector mounted thereon; a tracking systemthat measures a robot base position indicative of a position of therobot base relative to the environment; and, a control system that:acquires an indication of an end effector destination; determines arobot base position using signals from the tracking system; calculatesan end effector path extending to the end effector destination at leastin part using the robot base position; generates robot control signalsbased on the end effector path; applies the robot control signals to therobot arm to cause the end effector to be moved along the end effectorpath towards the destination; and, repeats steps (ii) to (vi) to movethe end effector towards the end effector destination.

It will be appreciated that the broad forms of the invention and theirrespective features can be used in conjunction and/or independently, andreference to separate broad forms is not intended to be limiting.

BRIEF DESCRIPTION OF THE DRAWINGS

Various examples and embodiments of the present invention will now bedescribed with reference to the accompanying drawings, in which: —

FIG. 1A is a schematic diagram illustrating a first example of a systemfor performing interactions within a physical environment;

FIG. 1B is a schematic diagram of a second example of a system forperforming interactions within a physical environment;

FIG. 1C is a schematic plan view of the system of FIG. 1B;

FIG. 2 is a schematic diagram of an example of a control system for thesystems of FIGS. 1A to 1C;

FIG. 3 is a flowchart of an example of a process for performing aphysical interaction;

FIG. 4 is a flow chart of an example of a robot base tracking process;

FIG. 5A is a schematic diagram illustrating an example of the robot basetracking process of FIG. 4;

FIG. 5B is a schematic plan view illustrating an example of the robotbase tracking process of FIG. 4;

FIG. 6 is a flow chart of an example of a process for calculating arobot base path;

FIGS. 7A to 7G are schematic diagrams illustrating an example of theprocess for calculating a robot base path;

FIGS. 8A to 8E are schematic diagrams illustrating an example of aninteraction performed in an interaction window;

FIG. 9 is a flowchart of an example of a process for controlling robotbase movement in accordance with a calculated robot base path;

FIG. 10 is a flowchart of a first example of a process for controlling arobot arm to provide end effector stabilisation;

FIGS. 11A and 11B are schematic diagrams illustrating an example of thecontrol process of FIG. 10 to provide the end effector at a staticposition;

FIGS. 11C and 11D are schematic diagrams illustrating an example of thecontrol process of FIG. 10 to move an end effector along an end effectorpath;

FIGS. 11E and 11F are schematic diagrams illustrating an example of thecontrol process of FIG. 10 to move the robot base along a robot basepath and the end effector along an end effector path;

FIG. 12 is a flowchart of a second example of a process for controllinga robot arm to provide end effector stabilisation;

FIGS. 13A to 13C are schematic diagrams illustrating an example of thecontrol process of FIG. 12 to provide the end effector at a staticposition;

FIG. 14 is a flowchart of a third example of a process for controlling arobot arm to provide end effector stabilisation;

FIGS. 15A and 15B are schematic diagrams illustrating an example of thecontrol process of FIG. 14 to provide the end effector at a staticposition;

FIGS. 15C and 15D are schematic diagrams illustrating an example of thecontrol process of FIG. 14 to move an end effector along an end effectorpath;

FIGS. 15E and 15F are schematic diagrams illustrating an example of thecontrol process of FIG. 14 to move the robot base along a robot basepath and the end effector along an end effector path;

FIGS. 16A to 16C are a flowchart of a specific example of an endeffector and robot base control process;

FIG. 17 is a flowchart of an example of a tracking system failurecontrol process;

FIG. 18 is a flowchart of an example of a tracking system failuredetection process;

FIG. 19 is a schematic view of an implementation of an inventionaccording to a first embodiment;

FIG. 20 is a schematic view of an implementation of an inventionaccording to a second embodiment;

FIG. 21 is a view of the tracker system for interfacing to control theposition of an end effector on the end of a boom according to anembodiment of the invention;

FIG. 22 is a view of the tracker system for interfacing to control theposition of an end effector on the end of a boom according to anembodiment of the invention;

FIG. 23 is a graph showing implementation of damping of movement whenstabilisation of the end effector is switched between a ground basedfirst state and a machine based second state;

FIG. 24 is a view showing operation of an embodiment showing machinebased second state operation;

FIG. 25 is a view showing operation of the embodiment of FIG. 24switched to ground based first state operation;

FIG. 26 is a top plan view showing use of an embodiment being a mobileblock laying machine incorporating the control system of the invention,in use to build a sound proofing wall along a freeway/motorway;

FIG. 27 is a side view showing use of a boom with a robotic arm mountedto an oil rig, in use to transfer items from a vessel subject tomovement in ocean swell; and

FIG. 28 is a view of detail of the embodiment illustrated in FIG. 27;and

FIG. 29 is a view showing use of a boom with a robotic arm mounted to anoil rig, in use to transfer items from a supply vessel subject tomovement in ocean swell.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following description explains a number of different systems andmethods for performing interactions within an environment. For thepurpose of illustration, the following definitions apply to terminologyused throughout.

The term “interaction” is intended to refer to any physical interactionthat occurs within, and including with or on, an environment. Exampleinteractions could include placing material or objects within theenvironment, removing material or objects from the environment, movingmaterial or objects within the environment, modifying, manipulating, orotherwise engaging with material or objects within the environment,modifying, manipulating, or otherwise engaging with the environment, orthe like. Further examples of interactions will become apparent from thefollowing description, and it will be appreciated that the techniquescould be extended to a wide range of different interactions, andspecified examples are not intended to be limiting. Furthermore, in someexamples, interactions may comprise one or more distinct steps. Forexample, when brick laying, an interaction could include the steps ofretrieving a brick from a brick supply mechanism and then placing thebrick in the environment.

The term “environment” is used to refer to any location, region, area orvolume within which, or on which, interactions are performed. The typeand nature of the environment will vary depending on the preferredimplementation and the environment could be a discrete physicalenvironment, and/or could be a logical physical environment, delineatedfrom surroundings solely by virtue of this being a volume within whichinteractions occur. Non-limiting examples of environments includebuilding or construction sites, parts of vehicles, such as decks ofships or loading trays of lorries, factories, loading sites, ground workareas, or the like, and further examples will be described in moredetail below.

A robot arm is a programmable mechanical manipulator. In thisspecification a robot arm includes multi axis jointed arms, parallelkinematic robots (such as Stewart Platform, Delta robots), sphericalgeometry robots, Cartesian robots (orthogonal axis robots with linearmotion) etc.

A boom is an elongate support structure such as a slewing boom, with orwithout stick or dipper, with or without telescopic elements,telescoping booms, telescoping articulated booms. Examples include cranebooms, earthmover booms, truck crane booms, all with or without cablesupported or cable braced elements. A boom may also include an overheadgantry structure, or cantilevered gantry, or a controlled tensile truss(the boom may not be a boom but a multi cable supported parallelkinematics crane (see PAR systems, Tensile Truss—Chernobyl Crane)), orother moveable arm that may translate position in space.

An end effector is a device at the end of a robotic arm designed tointeract with the environment. An end effector may include a gripper,nozzle, sand blaster, spray gun, wrench, magnet, welding torch, cuttingtorch, saw, milling cutter, router cutter, hydraulic shears, laser,riveting tool, or the like, and reference to these examples is notintended to be limiting.

TCP is an abbreviation of tool centre point. This is a location on theend effector (or tool), whose position and orientation define thecoordinates of the controlled object. It is typically located at thedistal end of the kinematic chain. Kinematic chain refers to the chainof linkages and their joints between the base of a robot arm and the endeffector.

CNC is an abbreviation for computer numerical control, used forautomation of machines by computer/processor/microcontroller executedpre-programmed sequences of machine control commands.

The application of coordinate transformations within a CNC controlsystem is usually performed to allow programming in a convenientcoordinate system. It is also performed to allow correction of workpieceposition errors when clamped in a vice or fixture on a CNC machiningcentre.

These coordinate transformations are usually applied in a static senseto account for static coordinate shifts or to correct static errors.

Robots and CNC machines are programmed in a convenient Cartesiancoordinate system, and kinematic transformations are used to convert theCartesian coordinates to joint positions to move the pose of the robotor CNC machine.

Measuring the position of a robot arm end effector close to the TCP inreal time increases the accuracy of a robot. This is performed on staticend effectors on robots used for probing and drilling. This is achievedby a multi-step process of moving to the programmed position, taking aposition measurement, calculating a correction vector, adding thecompensation vector to the programmed position and then moving the TCPto the new position. This process is not done in hard real time andrelies on a static robot arm pose.

Examples of systems for performing interactions within physicalenvironments will now be described with reference to FIGS. 1A to 1C andFIG. 2.

In the example of FIG. 1A the system 100 includes a robot assembly 110including a robot base 111, a robot arm 112 and an end effector 113. Therobot assembly 110 is positioned relative to an environment E, which inthis example is illustrated as a 2D plane, but in practice could be a 3Dvolume of any configuration. In use, the end effector 113 is used toperform interactions within the environment E, for example to performbricklaying, object manipulation, or the like.

The system 100 also includes a tracking system 120, which is able totrack the robot assembly movement, and in one particular example,movement of the robot base relative to the environment. In one example,the tracking system includes a tracker base 121, which is typicallystatically positioned relative to the environment E and a tracker target122, mounted on the robot base 111, allowing a position of the robotbase 111 relative to the environment E to be determined.

In one example, the tracking system 120 includes a tracking base 121including a tracker head having a radiation source arranged to send aradiation beam to the target 122 and a base sensor that senses reflectedradiation. A base tracking system is provided which tracks a position ofthe target 122 and controls an orientation of the tracker head to followthe target 122. The target 122 typically includes a target sensor thatsenses the radiation beam and a target tracking system that tracks aposition of the tracking base and controls an orientation of the targetto follow the tracker head. Angle sensors are provided in the head andthe target that determine an orientation of the head and targetrespectively. A tracker processing system determines a relative positionof the tracker base and target in accordance with signals from thesensors, specifically using signals from the angle sensors to determinerelative angles of the tracker and target, whilst time of flight of theradiation beam can be used to determine a physical separation. In afurther example, the radiation can be polarised in order to allow anorientation of the base relative to the tracking head to be determined.Although a single tracking system 120 including a head and target isshown, this is not essential and in other examples multiple trackingsystems and/or targets can be provided as will be described in moredetail below.

In one particular example, the tracking system is a laser trackingsystem and example arrangements are manufactured by API (Radian and OT2with STS (Smart Track Sensor)), Leica (AT960 and Tmac) and Faro. Thesesystems measure position at 300 Hz, or 1 kHz or 2 kHz (depending on theequipment) and rely on a combination of sensing arrangements, includinglaser tracking, vision systems using 2D cameras, accelerometer data suchas from a tilt sensor or INS (Inertial navigation System) and can beused to make accurate position measurements of position, with dataobtained from the laser tracker and active target equating to positionand optionally orientation of the active target relative to theenvironment E. As such systems are known and are commercially available,these will not be described in any further detail.

It will also be appreciated that other position/movement sensors, suchas an inertial measurement unit (IMU) can also be incorporated into thesystem, as will be described in more detail below.

A control system 130 is provided in communication with the trackingsystem 120 and the robot assembly 110 allowing the robot assembly to becontrolled based on signals received from the tracking system. Thecontrol system typically includes one or more control processors 131 andone or more memories 132. For ease of illustration, the remainingdescription will make reference to a processing device and a memory, butit will be appreciated that multiple processing devices and/or memoriescould be used, with reference to the singular encompassing the pluralarrangements. In use the memory stores control instructions, typicallyin the form of applications software, or firmware, which is executed bythe processor 131 allowing signals from the tracking system 120 androbot assembly 110 to be interpreted and used to control the robotassembly 110 to allow interactions to be performed.

An example of the control system 130 is shown in more detail in FIG. 2.

In this example the control system 230 is coupled to a robot armcontroller 210, a tracking system controller 220 and a boom controller240. The robot arm controller 210 is coupled to a robot arm actuator 211and end effector actuator 212, which are able to control positioning ofthe robot arm 112 and end effector 113, respectively. The trackingsystem controller 220 is coupled to the tracking head 221 and target222, allowing the tracking system to be controlled and relativepositions of the tracking head 221 and target 222 to be ascertained andreturned to the control system 230. The boom controller 240 is typicallycoupled to boom actuators 241, 242 which can be used to position theboom and hence robot base. A second tracking system 225 may also beprovided, which includes sensors 226, such as inertial sensors,optionally coupled to a controller or processor. It is to be understoodthat in practice the robot arm, end effector and boom will have multipleactuators such as servo motors, hydraulic cylinders and the like toeffect movement of their respective axes (i.e. joints) and reference tosingle actuators is not intended to be limiting.

Each of the robot arm controller 210, tracking system controller 220,second tracking system 225 and boom controller 240 typically includeelectronic processing devices, operating in conjunction with storedinstructions, and which operate to interpret commands provided by thecontrol system 230 and generate control signals for the respectiveactuators and/or the tracking system and/or receive signals from sensorsand provide relevant data to the control system 230. The electronicprocessing devices could include any electronic processing device suchas a microprocessor, microchip processor, logic gate configuration,firmware optionally associated with implementing logic such as an FPGA(Field Programmable Gate Array), or any other electronic device, systemor arrangement. It will be appreciated that the robot arm controller210, tracking system controller 220 and boom controller 240 typicallyform part of the boom assembly, robot assembly and tracking system,respectively. As the operation of such systems would be understood inthe art, these will not be described in further detail.

The control system 230 typically includes an electronic processingdevice 231, a memory 232, input/output device 233 and interface 234,which can be utilised to connect the control system 230 to the robot armcontroller 210, tracking system controller 220 and boom controller 240.Although a single external interface is shown, this is for the purposeof example only, and in practice multiple interfaces using variousmethods (eg. Ethernet, serial, USB, wireless or the like) may beprovided.

In use, the processing device 231 executes instructions in the form ofapplications software stored in the memory 232 to allow the requiredprocesses to be performed. The applications software may include one ormore software modules, and may be executed in a suitable executionenvironment, such as an operating system environment, or the like.

Accordingly, it will be appreciated that the control system 230 may beformed from any suitable processing system, such as a suitablyprogrammed PC, computer server, or the like. In one particular example,the control system 230 is a standard processing system such as an IntelArchitecture based processing system, which executes softwareapplications stored on non-volatile (e.g., hard disk) storage, althoughthis is not essential. However, it will also be understood that theprocessing system could be any electronic processing device such as amicroprocessor, microchip processor, logic gate configuration, firmwareoptionally associated with implementing logic such as an FPGA (FieldProgrammable Gate Array), or any other electronic device, system orarrangement.

It will also be appreciated that the above described arrangements arefor the purpose of illustration only and practice a wide range ofdifferent systems and associated control configurations could beutilised. For example, it will be appreciated that the distribution ofprocessing between the controllers and/or control system could varydepending on the preferred implementation.

For the purpose of the following examples, reference will be made to anenvironment coordinate system ECS, which is static relative to theenvironment E, and a robot base coordinate system RBCS, which is staticrelative to the robot base 111. Additionally, some examples will makereference to a robot base actuator coordinate system BACS, which is acoordinate system used to control movement of the robot base, forexample to control movement of the boom assembly.

In practice, in the above described examples, the robot base 111undergoes movement relative to the environment E. The nature of themovement will vary depending upon the preferred implementation. Forexample, the robot base 111 could be static, with the environment Emoving. A good example of this is when a robot arm is provided on a dockand is attempting to interact with objects present on the deck of aboat, which is undergoing movement relative to the dock. However, itwill be appreciated that similar relative movement will arise in a rangeof different circumstances.

Alternatively, in the example shown in FIG. 1B, the robot base 111 issupported by a robot base actuator 140, which can be used to move therobot base. In this example, the robot base actuator is in the form of aboom assembly including a boom base 141, boom 142 and stick 143. Theboom is typically controllable allowing a position and/or orientation ofthe robot base to be adjusted. The types of movement available will varydepending on the preferred implementation. For example, the boom base141 could be mounted on a vehicle allowing this to be positioned andoptionally rotated to a desired position and orientation. The boom andstick 142, 143 can be telescopic arrangements, including a number oftelescoping boom or stick members, allowing a length of the boom orstick to be adjusted. Additionally, angles between the boom base 141 andboom 142, and boom 142 and stick 143, can be controlled, for exampleusing hydraulic actuators, allowing the robot base 111 to be provided ina desired position relative to the environment E. Such operation istypically performed in the robot base actuator coordinate system BACS,although this is not essential as will become apparent from theremaining description.

An example of a system of this form for laying bricks is described in WO2018/009981 the content of which is incorporated herein by crossreference. It will be appreciated however that such arrangements are notlimited to bricklaying, but could also be utilised for other forms ofinteractions.

Depending on the implementation, the boom assembly can have asignificant length, so for example in the case of a constructionapplication, the boom may need to extend across a construction site andcould have a length of tens of meters. In such circumstances, the boomis typically subject to a variety of loads, including forces resultingfrom movement of the boom and/or robot arm, wind loading, machineryvibrations, or the like, which can in turn induce oscillations or othermovement in the end of the boom, in turn causing the robot base to moverelative to the environment. Such movement will be referred to generallyas unintentional movement. Additionally, as described above, the robotbase can be moved in a controlled manner by actively moving the boom andsuch movement will be referred to generally as intentional movement.

In any event, it will be appreciated that in both of the above describedexamples, the robot base and hence the robot base coordinate system RBCSmoves relative to the environment and hence environment coordinatesystem ECS, which substantially complicates the control process, and inparticular the ability of the end effector to be accurately positionedso as to perform an interaction within the environment. In this regard,in normal robot applications, the end effector is controlled in therobot base coordinate system RBCS, whilst the end effector needs to bepositioned in the environment coordinate system ECS, and as the movementresults in the two coordinate systems moving relative to each other,this makes accurately positioning the end effector difficult.

An example of the process for performing an interaction within theenvironment E will now be described with reference to FIG. 3.

For the purpose of the following explanation reference will be made to aterm “destination”. The term is intended to refer to a position andoptionally orientation (in combination referred to as a pose) at whichthe end effector 113 is to be provided, either as part of performing aninteraction or otherwise. For example, the destination could correspondto the location within the environment at which the interaction is tooccur. However, this is not essential, alternatively the destinationcould correspond to any position through which the end effector shouldpass, in effect defining multiple destinations leading to a finaldestination. For example, an interaction may involve sequences of endeffector movements, optionally forming part of different steps, and theterm destination could refer to any position forming part of thedifferent steps. Thus, the term destination should therefore beinterpreted to refer to any particular point at which the end effectoris to be positioned and in some examples, a destination could be astatic point at which an end effector is to be maintained for a periodof time for example while other processes are performed, whereas inother cases the destination could be transitory and correspond to apoint on a path through which the end effector is to traverse.

In this example, one or more destination positions are determined atstep 300. The manner in which this is achieved will vary depending onthe preferred implementation. In one example, destinations can beretrieved from a database or other data store, received from anotherprocessing system, determined based on signals from sensors or userinput commands, or the like. For example, end effector destinationscould be derived from a plan, such as a construction plan for abuilding, in which case the plan could be retrieved and the destinationsderived from the plan. In this regard, the construction plan mayidentify positions at which objects such as bricks are to be placed inorder for a building to be constructed. In this example, the destinationpositions can simply be retrieved from the plan.

However, this is not essential and alternatively, destination positionsmay need to be ascertained in other manners. For example, it may benecessary to retrieve an object from an environment, in which case thedestination of the end effector corresponds to the object position. Inthis example, the object position may not be known in advance, in whichcase the position of the object may need to be detected, for exampleusing a camera based vision system, or other localisation system,allowing the detected position to be used in order to define thedestination position. In this regard, the object could be static ormoving, meaning whilst the destination is normally static relative tothe environment coordinate system ECS, in some examples, the destinationcould be moving.

It will also be appreciated that destinations could be determined inother appropriate manners, and the above described examples are notintended to be restrictive.

At step 310, a robot base path to allow for movement of the robot base111 is optionally planned. The robot base path may not be required, forexample in the event that the robot base 111 is static or alreadypositioned. However, it will be appreciated that the robot base path maybe used to move the robot base 111 to different positions within orrelative to the environment E, in order to allow the end effector 113 tobe more conveniently provided at the respective destination. The mannerin which the base path is calculated will vary depending upon thepreferred implementation and examples will be described in more detailbelow.

At step 320, an end effector path is planned to move the end effector113 to the destination. The end effector path is typically planned basedon a planned position of the robot base 111 relative to the environmentE, for example to take into account movement of the robot base 111 alongthe robot base path. The end effector path may extend from an expectedprevious position of an end effector 113, for example at the completionof a previous interaction or other step, or could be calculated in realtime based on a current end effector position. It will be appreciatedthat in the event that the destination is based on a current position,the end effector path could be a null path with zero length, with thisbeing used for the purpose of positioning the end effector 113statically relative to the environment E.

At step 330, the robot base 111 is optionally moved based on the robotbase path, for example by controlling the boom assembly 140, or anotherform of robot base actuator. This process is typically performed in therobot base actuator coordinate system BACS, although this is notessential and robot base path planning and/or control of robot basemovement could be performed in other coordinate systems. During and/orfollowing this process, the commencement of end effector movement isperformed at step 340, causing the end effector to start moving alongthe end effector path, assuming this is required. This process istypically performed in the robot base coordinate system RBCS, althoughthis is not essential and end effector path planning and/or controlcould be performed in other coordinate systems.

As movement of the end effector 113 is performed, or otherwise if theend effector 113 is being held at a static position relative to theenvironment E, movement of the robot base is monitored at step 350,using the tracking system 120 to continuously detect a position of therobot base 111 relative to the environment E. This is used to adjust endeffector movement, for example by adjusting pose of robot arm, at step360 to ensure the destination position is reached.

In this regard, the robot base may undergo unintentional movementrelative to the environment E, either due to a shift in the environment,or due to an unexpected movement of the robot base, resulting fromvibrations in or wind loading of the boom, or the like. Such motionsmean that the robot base may not be provided in an expected positionrelative to the environment, for example as a result of the robot base111 deviating from the calculated robot base path. In this example, bymonitoring movement of the robot base 111, such movements can becorrected for, ensuring that the end effector moves correctly along theend effector path to the destination position.

Thus, in one example, a robot base actuator is used to provide a coarsepositioning system, whilst the robot arm provides a fine positioningsystem to allow an end effector to be accurately positioned relative tothe environment. Operation is controlled by a control system that uses atracking system to measure a position and optionally orientation of therobot base in real time, with a measured position (and orientation) ofthe robot base being used to calculate an offset that is added as aposition transformation to the relative position of the fine positioningmechanism so that the end effector is positioned correctly relative tothe environment. Thus a large and relatively light and flexiblestructure can be used to approximately position a fast and accurate finepositioning mechanism, which can be accurately controlled in real timeallowing an end effector to be moved relative to an environment in anaccurate and fast motion.

This form of operation is referred to by the applicant as dynamicstabilisation technology (DST) and is described in prior publicationsincluding U.S. Pat. No. 8,166,727, WO2009/026641, WO2009/026642,WO2018/009981 and WO2018/009986, the contents of which are incorporatedherein by cross reference.

It will also be appreciated that DST can also be used to account forintentional movement of the robot base, for example to account for thefact that the robot base 111 may be traversing a robot path whilst aninteraction is performed.

An example of a number of different aspects of the above describedsystem will now be described in further detail. These different aspectsof the system can be used independently or can be used in conjunctiondepending on the preferred implementation. It will be appreciated fromthis that reference to separate aspects should not be consideredlimiting and that aspects can be used in any number of differentcombinations, depending on the preferred implementation and the scenarioin which the system is used.

In one aspect a process for controlling the robot base is provided andan example of this will now be described in more detail with referenceto FIG. 4.

For the purpose of this example, it is assumed that the robot base canbe moved relative to the environment using a robot base actuator. Thenature of the actuator and manner in which this is performed can varydepending on the preferred implementation. In one example, the robotbase actuator could be a boom assembly 140 similar to that describedabove with respect to FIGS. 1B and 1C. However, any form of robot baseactuator could be provided and this could include a vehicle with therobot base being mounted on the vehicle, or could include the use of acrane or other similar arrangement for suspending the robot assemblyabove a work environment, or could include the use of self powered robotbases, for example including wheels or tracks, or the like.

In this example, at step 400 the control system acquires an indicationof an end effector destination defined relative to the environmentcoordinate system ECS. As previously described the end effectordestination could be determined in any number of manners and this couldinclude retrieving the destination from a plan, based on signalsreceived from a vision system that locates an object relative to theenvironment, or the like.

At step 410, a tracking target position is determined at least in partusing signals from the tracking system 120. The tracking target positionrepresents a position of the target 122, relative to the tracking base121, and hence the environment E. Thus the target position representsthe position of the target 122 in the environment coordinate system ECS.

At step 420 the control system determines a virtual robot base position.The virtual robot base position is offset from the actual physical robotbase and is defined at least partially in accordance with an endeffector position. An example of this is shown in FIG. 5A which shows asystem similar to that described above with respect to FIG. 1B, withlike components indicated by similar reference numerals increased by400.

In this example, a robot base 511 is positioned using a boom assembly540 having a boom base 541 and boom and stick 542, 543. The robot base511 has a tracker 522 mounted thereon whose position is tracked usingthe tracking base 521 provided relative to the environment E. In thisexample, the robot arm 512 is shown provided in a reference position,with the end effector 513 provided at a reference position relative tothe robot base.

The end effector reference position can be arbitrarily defined, but istypically based on one or more of an operative position indicative of aposition of the end effector 513 when performing an interaction in theenvironment, a pre-operative position indicative of a position of theend effector 513 prior to commencing an interaction in the environment,or a default position indicative of a position of the end effector 513following performing an interaction in the environment. Thus, thereference position is a typical position of the end effector, which isused at some point before, during or after an interaction is performed.

At step 430, the control system (not shown) uses the virtual robot baseposition and end effector destination to calculate a robot base pathextending from the current robot base virtual position to the endeffector destination.

In this regard, the position of the tracker target 522 is known in therobot base actuator coordinate system BACS by virtue of the robot baseactuator kinematics, and in particular the boom kinematics, and theknown location of the tracker target 522 on the robot base 511. Thus asthe tracker target 522 position is known in the environment coordinatesystem ECS and the robot base actuator coordinate system BACS, this canbe used to allow geometric transformations to transform other positionsbetween these coordinate systems.

Additionally, in this example, the tracker target 522 is offset from thereference end effector location, and hence reference robot base positionby offsets Z₁ and X₁. It will be appreciated that other offsets may alsoapply, for example a Y axis offset, as well as rotational offsets, mayalso be present, but not shown in this example for clarity. Accordingly,this allows the virtual robot base position to be known in the differentcoordinate systems.

At step 440, the control system generates robot base control signalsbased on the calculated path, and uses these to move the robot base atstep 450, for example by controlling the boom assembly 540.

It will be appreciated that as control is typically performed in therobot base actuator coordinate system BACS, the robot base path istypically calculated in the robot base actuator coordinate system BACS,in which case the control system uses the target position to calculate atransformation between the environment coordinate system ECS and therobot base actuator coordinate system BACS. Specifically, this involvestransforming the end effector destination into the robot base actuatorcoordinate system BACS, allowing the robot base path to be calculated inthe robot base actuator coordinate system BACS. However, it will beappreciated that this is not essential and alternatively the path couldbe calculated in the environment coordinate system ECS.

In any event, in the above described example, the control systemeffectively creates a virtual robot base position, which is a virtualposition of the robot base that is offset from the physical location ofthe robot base, and which is coincident with a reference position of theend effector. The control system then uses this virtual robot baseposition when controlling movement of the robot base, using a robot baseactuator, which can be beneficial in allowing the robot base to be moreeasily positioned in order to allow interactions to be performed.

For example, when calculating a robot base path, the control system cansimply acquire an end effector destination and then use thisdestination, together with the tracking target position, to define therobot base path, causing the robot base to traverse the environment to aposition which is suitable for the interaction to be performed. Inparticular this can be used to align the end effector with the endeffector destination, thereby reducing the complexity of the endeffector path and the need for significant control of the end effector.

A useful example of this is illustrated in FIG. 5B, which shows anexample in which the robot base actuator is a boom assembly mounted on avehicle 541, which acts as the boom base. In this regard, when it isrequired to perform interactions within the environment E, the vehicle541 may be located at any point relative to the environment E. In thisinstance, in order for the end effector to be positioned at adestination 551, the robot base 511 must be provided at a position thatis physically offset from the destination 551, by an offset O. However,this offset O varies depending on the position of the vehicle 541 andmust be calculated in the robot base actuator coordinate system BACS,which can be computationally complex. However, by controlling the robotbase actuator using a virtual robot base position, which is aligned withthe end effector 513, this automatically aligns the end effector 513with the end effector destination 551 as needed, irrespective of thepositioning of the vehicle relative to the environment.

Thus, utilising the virtual robot base position to control positioningof the robot base 511 means that the robot base 511 can simply be movedso that it is automatically offset from the destination 551 as needed.This means that irrespective of the original position of the robotactuator base, and in particular the boom base 541, the robot base 511is controlled so that the end effector 513 is effectively automaticallyaligned with the destination.

Additionally and/or alternatively, this can assist with path planning.For example, path planning and/or tracking of movement of the robot baseusing a virtual robot base position aligned with the end effector 513can help avoid collisions of the end effector 513 with the environmentor objects or material provided therein.

As mentioned, the virtual robot base position is typically defined to becoincident with a reference end effector position, such as an operativeposition, a pre-operative position, or a default post-operativeposition. It will be appreciated that the particular end effectorposition selected will vary depending upon the preferred implementation,and that other end effector positions could also be used.

In the current example, the robot base includes a head mounted to a boomwith the boom in turn being controlled by a boom actuator from a boomactuator base. In one particular example the boom base is attached to avehicle, with the virtual robot base position being offset from therobot base and defined at least partially in accordance with an endeffector position to allow the vehicle to be provided in differentpositions relative to the environment.

Whilst the above example has focused on robot base position, it will beappreciated that this could also take into account orientation, in whichcase the robot base pose will be calculated as a virtual robot basepose, which is physically offset from the robot base, and aligned withan end effector pose.

In one aspect a process for planning a robot base path is provided andan example of this will now be described in more detail with referenceto FIG. 6.

In this example, a number N of next end effector destinations aredetermined at step 600. As previously discussed, this can be achieved inany appropriate manner such as retrieving end effector destinations froma plan, detecting objects in an environment, or the like. The number ofend effector destinations that are selected will vary depending on thepreferred implementation and the nature of the interactions and planningperformed, but typically this will be at least 5, and more typically atleast 10, and in one preferred example about 20.

At step 605 the control system acquires tracking system signals and usesthese to determine a current robot base position at step 610. Aspreviously described, the robot base position may be a virtual robotbase position which is offset from the physical robot base, for exampleto align this with an end effector location.

At step 615 a robot base path is calculated, with this typically beingperformed in a robot base actuator coordinate system BACS, as describedin the previous example. In this example, the robot base path isconfigured to allow substantially continuous movement of the robot basealong the robot base path in accordance with a robot base velocityprofile, which defines the robot base velocity along the path.

Once planned, the robot base path can be executed at step 620 bygenerating robot base control signals based on the robot base path, withthese being applied to the robot base actuator, such as the boomassembly, to cause the robot base 511 to be moved.

Optionally, at step 625 it is determined if an interaction is beingcompleted, for example by having the end effector reach a destination,and if not execution of the robot base path continues. Otherwise, oncethe interaction is complete, the process returns to step 600 to allow anext N end effector destinations to be determined, so that the path isconstantly updated as end effector destinations are reached.

Accordingly, the above described arrangement calculates a robot basepath by examining a next N destinations and calculating a path based onthose destinations. Taking into account a number of destinations and notjust a next immediate destination, allows the path to be planned toavoid sudden changes in speed and/or direction of movement, allowing forsubstantially continuous movement along the path length.

In particular, the path can be calculated so that the path shape andvelocity profile, are carefully controlled to minimise changes in robotbase velocity, which in turn can be used to avoid discontinuities, suchas stepwise or sharp velocity changes. Sudden velocity changes, forexample increasing or decreasing the speed of the robot base movement,or changing the direction of movement, can induce vibrations within therobot base actuator, such as the boom arm of a boom assembly. This inturn can lead to greater unintentional movement of the robot base,including more movements and/or movements of larger magnitude, making itmore difficult for the DST to correct for movement of the robot base andensure the end effector is provided at a correct position.

In order to minimise the magnitude of velocity changes, including speedand/or direction changes, a number of different approaches can be used.In one example, the robot base path is curved and/or configured to allowthe robot base to be moved gradually whilst interactions are performed,so that the robot base does not need to be halted.

An example of the process for calculating a robot base path will now bedescribed in further detail with reference to FIGS. 7A to 7G.

In this regard, as described above a number of destinations areacquired, with an example of five end effector destinations 751.1,751.2, 751.3, 751.4, 751.5 being shown relative to the environment E inFIG. 7A. It will be appreciated that five end effector destinations onlyare shown for illustration and in practice a greater number may beexamined. Next, the control system calculates path segments 753.1,753.2, 753.3, 753.4 interconnecting the end effector destinations 751.1,751.2, 751.3, 751.4, 751.5, with these typically being in the form ofstraight lines extending directly between the end effector destinations751.1, 751.2, 751.3, 751.4, 751.5, as shown in FIG. 7B.

The interconnected path segments 753.1, 753.2, 753.3, 753.4 then undergosmoothing to generate the robot base path and an example of this isshown in FIG. 7C, in which transitions between adjacent path segments,and in particular points where the straight segments of the pathsconnect at angles, are curved.

However it will be appreciated that this represents a very basicsmoothing approach, and more aggressive smoothing approaches can beused, for example by deviating the path from the original straight pathsegments, and an example of this is shown in FIG. 7D.

In the example of FIG. 7D, it is noted that the path is constrained topass through each of the end effector destinations 751.1, 751.2, 751.3,751.4, 751.5. However, this is not essential, and alternatively, thepath can be constrained so that it always passes within a set distanceof the end effector destinations 751.1, 751.2, 751.3, 751.4, 751.5. Inone example, as shown in FIG. 7E, this is achieved by definingboundaries 754 a set distance from the straight path segments 753.1,753.2, 753.3, 753.4 which interconnect the end effector destinations751.1, 751.2, 751.3, 751.4, 751.5, with the resulting path beingconstrained to be located within the boundaries 754. The magnitude ofthe set distance of the boundaries 754 can be defined based onkinematics of the robot arm, with this being performed to ensure thatthe end effector is able to successfully reach the respectivedestinations assuming the robot base, and in particular the virtualrobot base, follows the defined robot base path.

Accordingly, in this example, the robot base path passes within a setdistance of each destination and/or is provided within a set distance ofstraight lines interconnecting adjacent destinations.

As part of the above described approach, the control system cancalculate robot base path velocities for each of a plurality of pathsegments and then perform smoothing of the robot base path velocities togenerate the robot base velocity profile, in particular so the velocityvaries progressively along the path, thereby requiring minimum amountsof acceleration. For example, if two end effector destinations arepositioned closely, such as the end effector destinations 751.2, 751.3,then this might require that the path segment 753.2 has a lower robotbase path velocity than that of surrounding paths.

In one example, calculation of the robot base path is performed takinginto account an end effector path length, an end effector velocityprofile associated with the end effector path, robot kinematics and/ordynamics, as well as robot actuator kinematics and/or dynamics. Forexample, the path would typically be calculated taking into account areach of the end effector, so that the path is within reach of thedestination, thereby ensuring that the robot arm is capable ofperforming interactions assuming the robot base follows the robot basepath. Similarly, this will also take into account dynamics andkinematics of the robot base actuator, to ensure the actuator is capableof implementing the robot base path.

It will be appreciated that in the above described example, the processis described assuming a virtual robot base position aligned with the endeffector is used, similar to that described above with respect to FIGS.4, 5A and 5B. In the event that such an arrangement is not used, then anoffset would need to be introduced to calculate a desired robot baseposition from the end effector destination.

An example of this is shown in FIG. 7G, in which an offset 758.1, 758.2,758.3, 758.4, 758.5 is added to the end effector destination 751.1,751.2, 751.3, 751.4, 751.5 to represent the physical offset of the robotbase 111 from the end effector 113. This leads to a number of robot basedestinations, 757.1, 757.2, 757.3, 757.4, 757.5, which can then be usedto calculate a robot base path 759, and it will be appreciated that thiscan be performed in a similar manner to that described above, albeitperforming the calculation on the robot base destinations 757.1, 757.2,757.3, 757.4, 757.5 as opposed to the end effector destinations 751.1,751.2, 751.3, 751.4, 751.5.

In this example, the robot base actuator rotates about an axis A,meaning each offset 758.1, 758.2, 758.3, 758.4, 758.5, whilst having thesame length, will be at a different orientation, and hence unique foreach end effector destination. This further highlights the benefit ofusing the above described virtual robot base position when calculatingrobot base paths. In any event, it will be appreciated that otherwisethe robot base path can be calculated using similar techniques to thoseoutlined above with respect to the use of the end effector destinationsand virtual robot base position and this will not therefore be describedin any further detail.

Path planning can also take into account interaction dependencies. Inthis regard, interactions will typically have dependencies, so that forexample laying a particular brick may require that one or more adjacentbricks are laid first. In this instance, the control system typicallyretrieves interaction dependencies, which are generally defined as partof an interaction plan, such as a construction plan, and then calculatesthe robot base path in accordance with the interaction dependencies, forexample to ensure that interactions are not performed until dependencyrequirements are met.

Additionally and/or alternatively, path planning can take into accountan interaction time, indicative of a time to perform an interaction,which is then used to calculate the robot base path velocity profile andoptionally define an interaction window, which can then be used incontrolling the robot base dynamically. In this regard, interactionwindows typically correspond to a region of the environment surroundingthe end effector destination or robot base destination in which thevirtual robot base can be provided, whilst still allowing an interactionto be performed, and so this allows the velocity of the robot base as ittraverses the robot base path to be controlled, for example depending ona completion status of the interaction.

An example of this will now be described in more detail with referenceto FIGS. 8A to 8E. For the purpose of this example, explanation will bemade with reference to the virtual robot base position, with theinteraction window being calculated based on the end effector position,but it will be appreciated that the technique is equally applicable toarrangements not using the virtual robot base and/or interaction windowsdefined relative to a robot base destination.

In this example, a robot assembly having a robot base 811, robot arm 812and end effector 813 is shown. An interaction window 852 is definedrelative to an end effector destination 851. As the robot base 811approaches the interaction window 852, movement of the end effectorcommences, so that the end effector starts moving along an end effectorpath towards the destination 851, as shown in FIG. 8B. The end effectorcan then perform an interaction as shown in FIG. 8C, as the robot base811 passes the destination 851, with the interaction being concluded asshown in FIG. 8D, and with the end effector returning to an originalposition as the robot base moves past the interaction window as shown inFIG. 8E.

The interaction windows are typically determined based on theinteraction time and a velocity, so that the time required to perform aninteraction, such as to pick up an object or place an object,corresponds to the time taken to traverse the interaction window at thedefined robot base path velocity profile.

In one particular example, interaction windows are defined based on aset distance surrounding a destination, derived for example based onrobot arm kinematics and/or dynamics such as the reach and or velocityof the end effector. An example of this is shown in FIG. 7F. In thisexample, multiple interaction windows 752.1, 752.2, 752.3, 752.4, 752.5are provided around the destinations 751.1, 751.2, 751.3, 751.4, 751.5.

In this particular instance the destinations 751.2, 751.3 aresufficiently close together that the interaction windows 752.2, 752.3would overlap, meaning a next interaction would need to start before aprevious interaction has concluded. To take this into account, theextent of each window is reduced to allow the windows to abut at a pointmidway between the adjacent destinations 751.2, 751.3. It will beappreciated that in this instance, the windows are shorter than forother destinations, and accordingly, the robot base path velocityprofile would need to be reduced to allow interactions to be performedwithin the interaction windows 752.2, 752.3 as compared to otherinteraction windows.

As an alternative to this however, a destination order could be altered,for example by omitting the destination 751.3 from the path and thenreturning to perform interaction at that destination at a later point intime. Whether this occurs will to some extent depend on whether or notthis is feasible, and in particular this may depend on interactiondependencies, as discussed above.

Having defined the interaction windows, these can then be used in orderto control movement of the robot base 811 and end effector 813 and inparticular to ensure an interaction is completed without requiring adiscrete velocity change. For example, the control system can monitorend effector interaction to determine a completion status, andselectively modify the robot base control signals to cause the robotbase to move at different velocities, depending on results of themonitoring.

In one particular example, when the robot base path includes aninteraction window associated with each end effector destination, as therobot base enters an interaction window the control system can controlthe robot arm to commence interaction and/or movement of the endeffector along an end effector path to the end effector destination. Thecontrol system can then monitor interaction by determining if theinteraction will be completed by the time the robot base approaches anexit to the interaction window, optionally progressively reducing therobot base velocity to ensure that the interaction is completed by thetime the robot base reaches the exit to the interaction window.

In one example, the interaction includes a number of steps, and whereinthe control system monitors the interaction by monitoring completion ofsteps. As part of this process, the control system determines an endeffector path for a next step and then generates control signals to movethe end effector to thereby complete the step.

An example of a control process using the above described path planningarrangement will now be described in more detail with reference to FIG.9.

In this instance, at step 900 a robot base path is calculated. This isperformed using the approached described above with respect to FIG. 6and this will not therefore be described in further detail.

At step 905, a current robot base position is determined using signalsfrom the tracking system, with this being used by the control system todetermine if an interaction window has been reached at step 910. If notthe movement of the robot base continues at step 915, with steps 905 to915 continuing until an interaction window is reached at step 920.

Following this an interaction associated with the interaction windowcommences. In this regard, interactions typically consist of a sequenceof steps, and may include moving the end effector to an end effectordestination and then returning the end effector to a starting position,home or reference position. For example, in the case of brick laying,the interaction could involve collecting a brick from a presentationmechanism mounted on the boom and/or robot base, moving the end effectorand brick to a destination in the environment to allow the brick to belaid, before returning the end effector to allow a next brick to becollected.

An end effector path associated with the next step is retrieved and/orcalculated as required at step 925, with the control system determiningif the interaction is proceeding on schedule at step 930. If not, therobot base speed is modified at step 935, so that the robot base isprogressively slowed to a velocity below that defined in the robot basepath velocity profile. This can be achieved in any manner, but in oneexample this is achieved by gradually scaling the velocity based on aproximity to an entry to and/or exit from the interaction window.

The end effector 813 and robot base 811 are moved at step 940, with thecontrol system determining if the step has been completed at step 945.If not, steps 930 to 945 are repeated until the step has been completed.

Once the step has been completed the control system determines if allsteps have been completed and if not goes on to select a next stepotherwise returning to step 900 to calculate a new robot base path.

Accordingly, the above described arrangement operates to calculate apath that avoids discontinuities and/or sudden or sharp changes indirection or speed, to thereby minimise unintentional movements of therobot base, such as unwanted oscillations or other movements.Additionally and/or alternatively, the above described approach usesinteraction windows to control the robot base speed during the processof performing interactions within the environment. In this regard, theinteraction window is defined together with a path velocity profile,based on a time taken to perform the interaction, so that theinteraction can be performed without deviating from the velocityprofile. In operation, completion of the interaction is monitored withmovement of the robot base along the robot base path being progressivelyslowed if the interaction is running behind schedule. This is performedto ensure that the interaction can be performed before the robot baseexits the interaction window.

As previously described, movement of the end effector is typicallycontrolled to take into account, and in particular correct for movementof the robot base, thereby enabling the end effector to be accuratelycontrolled within the environment coordinate system ECS, irrespective ofrelative movement between the environment and the robot base. Thus, suchDST dynamically adjusts the end effector in order to account formovement of the robot base, which can be used, for example, to keep theend effector static or moving along or in accordance with a defined pathwithin the environment, irrespective of movement of the robot base.

Dynamic stabilisation technology can be implemented utilising differentapproaches and three example mechanisms will now be described, withthese hereinafter being referred to as dynamic compensation, dynamiccoordinate system and dynamic path planning.

Dynamic compensation operates by generating a path correction andapplying the path correction when generating control signals thatcontrol the robot arm, so that the arm follows a modified path thatbrings the end effector back on to the original planned path.

Dynamic coordinate systems operate by calculating robot arm kinematicsin a moving coordinate system which tracks movement of the robot base,so that the end effector always has a correct position in theenvironment coordinate system ECS. This generally involves shifting theorigin of the robot arm kinematics, to ensure the end effector iscorrectly positioned.

Dynamic path planning involves recalculating end effector paths as therobot base and environment move relative to each other, so that the newpath ensures the end effector always progresses to the end effectordestination.

Accordingly, in one aspect a process for performing dynamic compensationis provided, and an example of this will now be described with referenceto FIG. 10, and making reference to the system of FIGS. 1B and 1C.

In this example, at step 1000 the control system 130 acquires an endeffector destination, which as will be appreciated can be achieved usingtechniques described above.

At step 1010, a reference robot base position is determined by thecontrol system 130, with this typically being performed relative to theenvironment coordinate system ECS. The reference robot base position canbe a current position and/or could be a position at a future point intime, and may therefore represent an expected position when the endeffector is to perform an interaction, such as positioning an objectwithin the environment.

An end effector path is then calculated by the control system 130 atstep 1020, with the path extending to the end effector destination. Thisprocess can be performed at least in part using the reference robot baseposition in order to take into account any movement from the currentrobot base position to the reference robot base position and/or totransform between the robot base and environment coordinate systemsRBCS, ECS, if this required. For example, the end effector path istypically calculated in the robot base coordinate system RBCS, as thisallows control signals for the robot arm to more easily map to themovement, meaning the end effector destination is transformed from theenvironment coordinate system ECS to the robot base coordinate systemRBCS. This is performed based on the relative position of the coordinatesystems when the robot base is positioned in the reference robot baseposition, taking into account that the relative position of the robotbase and environment coordinate systems RBCS, ECS will vary as the robotbase 111 moves along the robot base path. However, this is notessential, and alternatively the current end effector position could betransferred into the environment coordinate system ECS, allowing the endeffector path to be calculated in the environment coordinate system ECS.

Having calculated a path, at step 1030, a current robot base position isdetermined using signals from the tracking system. This is used tocalculate a correction which is indicative of a path modification atstep 1040. The nature of the correction and the manner in which this iscalculated will vary depending upon the preferred implementation but inone example this is in the form of a vector representing deviation ofthe current end effector position with respect to the end effector path,as determined based on movement of the robot base. For example, if therobot base 111 undergoes movement away from an expected robot baseposition, this will result in equivalent movement of the end effector113 away from the end effector path, which will need to be corrected inorder to ensure the end effector continues to traverse the path.

Robot control signals are generated by the control system 130 at step1050, based on the end effector path and the correction, with thesebeing applied to the robot arm to cause the end effector 113 to be movedin accordance with the end effector path and the correction, so that theend effector moves back to the end effector path and continues towardsthe destination at step 1060. Steps 1030 to 1060 are then repeated asneeded until the end effector has reached the destination.

Accordingly, the above described technique operates by calculating acorrection based on a deviation of the current measured robot baseposition from an expected robot base position, using the correction whengenerating robot control signals to thereby correct the position of theend effector. In one example, the robot base moves with a slower dynamicresponse, whilst the end effector moves with a faster dynamic response,so that movement of the end effector can be used to correct for movementof the robot base away from an expected robot base position.

A number of different example scenarios will now be described withreference to FIGS. 11A to 11F, to more clearly explain operation of thedynamic compensation in a number of different scenarios. These examplesshow an end effector 1113 attached to a robot arm 1112, which is in turnattached to a robot base (which is not shown for clarity). The followingexamples will illustrate the dynamic compensation mechanism operating intwo dimensions only, but it will be appreciated that this can extend tosix degrees of freedom, and reference to two dimensions only is notintended to be limiting.

In the example of FIGS. 11A and 11B, the end effector destination iscoincident with a current end effector position, meaning the calculatedend effector path is in fact a null path with zero path length. Such anarrangement would be used in order to maintain a static end effectorposition within the environment E.

In this example, an unintentional movement 1161 of the robot base, forexample caused by vibrations, wind loading of a boom, or the like, movesthe robot arm 1112 and hence end effector 1113. As a result, the endeffector 1113 is now offset from the destination 1151. In this instance,a correction is calculated based on the movement 1161, which generates apath correction, in this instance effectively creating a new path 1162,which causes the robot arm to move the end effector and counteract theunintentional movement 1161, thereby returning the end effector to thedestination 1151. In this regard, the pose of the robot arm will changein accordance with the unintentional movement of the robot base in orderto effect the path correction and bring the end effector 1113 back tothe destination 1151.

In the example of FIGS. 11C and 11D, the end effector 1113 is traversingalong an end effector path 1155 to destination 1151. In this instance,unintentional movement 1161 occurs whilst the robot arm issimultaneously moving along the path as shown by the arrow 1163. In thisinstance, the correction is calculated to cause the end effector to movein accordance with arrow 1162, with this being combined together with anext movement along the path 1164, resulting in a net movement 1165,which returns the end effector 1113 to the original path 1155.

A further example shown in FIGS. 11E and 11F involves moving the endeffector along an end effector path 1155, and simultaneously moving therobot base along a robot base path 1153. In this instance the referencerobot base position is shown in dotted lines in FIG. 11E, which is basedon the expected robot base position when the end effector 1113 reachesthe end effector destination 1151. In this instance, from the referencerobot base position, the end effector path 1155 is vertically down tothe destination 1151, and with a net path 1156 being formed from acombination of the end effector path 1155 and the robot base path 1153,resulting in net end effector movement from the current end effectorposition to the destination 1151.

In this instance as the robot base and end effector 1113 are moved alongthe net path, as shown at 1163, an unintentional movement arises asshown as 1161. In this instance a correction 1162 is calculated whichcombined with next path movement 1164, results in the end effectormoving along a path 1165, returning to the original net path 1156.

Accordingly, it will be appreciated that the above described processesoperate to correct for at least unintentional movement of the endeffector to thereby maintain the end effector 1113 at a desiredposition, or travelling in accordance with a desired path, within theenvironment coordinate system ECS, even though the end effector iscontrolled in the robot base coordinate system RBCS.

As mentioned above, in one preferred example, the control system 130calculates the end effector path in the robot base coordinate systemRBCS, whilst the end effector destination is typically defined in theenvironment coordinate system ECS. This involves having the controlsystem 130 determine a transformed end effector destination bytransforming the end effector destination from the environmentcoordinate system ECS to the robot base coordinate system RBCS, at leastin part using the reference robot base position. The control system 130can then calculate an end effector path extending to the transformed endeffector destination in the robot base coordinate system RBCS. It willbe appreciated however that this is not essential and alternatively pathcalculation can be performed in the environment coordinate system ECS.

In one example, the control system determines an end effector positionand then calculates the end effector path using the end effectorposition, so that the end effector path extends from the end effectorposition to the end effector destination. The end effector position istypically determined in a robot base coordinate system using robot armkinematics. In one example, the end effector position is the currentposition, but alternatively, the end effector position could be anexpected position when the robot base reaches the reference robot baseposition, in which case the end effector position can be determined bytransforming a current end effector position based on the referencerobot base position.

The correction is typically indicative of a deviation of the endeffector from the end effector path, which in turn is based on deviationof the robot base from an expected position. Accordingly, the controlsystem calculates a robot base deviation based on the current robot baseposition and an expected robot base position, and then calculates thecorrection based on the robot base deviation. The expected robot baseposition can be based on a reference robot base position or a positionthe robot base is expected to be in based on traversal of a robot basepath. Additionally, in situations where the end effector is being heldstationary within the environment, the expected robot base position canbe based on an initial or previous robot base position.

The reference robot base position is used to allow the calculation ofthe end effector path to take into account that the robot base isexpected to move between end effector movement commencing and thedestination being reached. Accordingly, while the reference robot baseposition can be a current or initial robot base position, more typicallythe reference robot base position is a predicted robot base position,based on movement of the robot base along a robot base path.Specifically, the reference robot base position is preferably anintended robot base position when the end effector reaches the endeffector destination. Thus it will be appreciated that the referencerobot base position could be calculated based on the expected positionof the robot base as the destination is reached, so that the endeffector moves along a direct path from the current position to the endeffector destination in the robot base coordinate system RBCS.

When the reference robot base position is based on the position duringinteraction, the compensation need only account for unintentionalmovement of the robot base away from a robot base path extending to thereference robot base position. Although it will be appreciated this isnot essential and alternatively the correction can take into accountboth unintentional and intentional movement. For example, the endeffector path could be calculated based on an initial robot baseposition, with movement along a robot base path being compensated forusing the end effector path.

In some circumstances it may be desirable to control the position of theend effector without using DST. An example of this arises when the endeffector is interacting with objects solely within the robot basecoordinate system RBCS, for example, to retrieve an object from adelivery mechanism mounted on the robot base. In this instance, as theobject and end effector both move with the robot base, this does notrequire DST to be active.

Accordingly, the DST mechanism may need to be activated and deactivated,for example activating DST as the end effector transitions fromcollecting an object in the robot base coordinate system RBCS to placingthe object in the environment E. As the robot base path might haveundergone significant movement between the end effector path beingcalculated and DST being activated, fully activating the compensationmechanism could result in a large correction being calculated, whichmight not be practical as a result of robot arm dynamics.

Accordingly, in one example, the control system 130 scales thecorrection based on a relative distance of the current end effectorposition from the end effector destination. In particular, scaling canbe used to effectively transition turning the DST on and off Whilst anyform of scaling could be used, the control system typically scales thecorrection using an S shaped curve, to progressively apply thecorrection. This gradually turns on the correction and reduces the rateof increase of the scaling as the end effector nears the destination,thereby reducing large end effector corrections.

In one particular example, the control system 130 moves the end effector113 between first and second end effector destinations defined in therobot base and environment coordinate systems RBCS, ECS respectively,with the control system scaling the correction based on the relativedistance of the current end effector position from the first and secondend effector destinations. Consequently, no correction is performed whenthe end effector is near the first end effector destination, whilst fullcorrection is performed when the end effector is near the second endeffector destination.

Throughout the above example, reference has been made to a robot baseand end effector position. However, it will be appreciated that DST canalso be applied to the orientation of the end effector, meaning ineffect the above described process is implemented based on the endeffector and robot base pose, and with the end effector destinationbeing in the form of an end effector pose.

In this particular example, the control system determines an endeffector pose relative to the robot base coordinate system, calculatesthe end effector path using the end effector pose and a reference robotbase pose in the environment coordinate system, determines a currentrobot base pose using signals from the tracking system and calculatesthe correction based on the current robot base pose. In this example,the correction is typically in the form of a vector indicative ofmovement in each of six degrees of freedom. The control system thencontrols the end effector pose, thereby providing correction in all sixdegrees of freedom.

Whilst the above example has focused on scenarios in which the robotbase moves, it will be appreciated that this is not essential and thesame techniques can be implemented when the robot base is static and theenvironment is moving relative to the robot base.

In one aspect a process for using a dynamic coordinate system isprovided, and an example of this will now be described with reference toFIG. 12.

In this example, an end effector destination is acquired by the controlsystem 130 at step 1200, using the techniques similar to those describedabove. At step 1210 the control system 130 determines a reference robotbase position, which is typically determined in the environmentcoordinate system ECS, and which again could correspond to a currentposition, a position at which an interaction is expected to occur, orthe like. At step 1220, an end effector path extending to the endeffector destination is determined at least in part using the referencerobot base position.

It will be appreciated that the above described steps 1200 to 1220 aregenerally similar to the equivalent steps previously described withrespect to FIG. 10. However, in this example whilst the end effectorpath could be calculated in the robot base coordinate system RBCS moretypically this is performed in the environment coordinate system ECSusing the reference robot base position.

At step 1230, the control system 130 determines a current robot baseposition using signals from the tracking system 120. This is used tocalculate robot arm kinematics at step 1240, so that the kinematics takeinto account the current robot position, and more typically a deviationfrom an expected robot base position. Specifically, in one example, therobot base position is used as an origin point of the robot armkinematics, so that as the robot base moves within the environmentcoordinate system, this allows the origin point of the robot armkinematics to be updated, allowing the robot arm to be controlled in theenvironment coordinate system.

At step 1250 control signals are generated based on the end effectorpath and the calculated robot arm kinematics, allowing the controlsystem to apply the control signals to the robot arm at step 1260,thereby causing the robot arm to move. Steps 1230 to 1260 can then berepeated as needed, for example until an end effector destination isreached.

Accordingly, in contrast to the previous example which calculated a pathcorrection indicative of a deviation of the end effector from a plannedpath, the above described example operates by modifying robot armkinematics. In one particular example this is achieved by shifting anorigin of the robot arm kinematic chain, based on movement of the robotbase from an expected robot base position, so that the origin shiftreflects movement of the robot base. This then modifies the positioningof the robot arm, so that the robot arm is controlled in a dynamiccoordinate system that moves relative to the environment coordinatesystem ECS and enables the end effector to remain on the end effectorpath. This has the benefit of avoiding the need to calculate pathcorrections, and thereby reducing the computational complexity ofperforming DST.

Irrespective of this however, the robot base moves with a slower dynamicresponse, whilst the robot arm and hence end effector moves with afaster dynamic response, so that movement of the robot arm can be usedto correct for movement of the robot base away from an expected robotbase position, so that the end effector can be maintained in a desiredposition.

A specific example correction will now be described with reference toFIG. 13A to 13C, which show an end effector 1313 that is attached to arobot arm 1312, extending from a robot base 1311. The following exampleillustrates the dynamic coordinate system mechanism operating in twodimensions only, but it will be appreciated that this can extend to sixdegrees of freedom, and reference to two dimensions only is not intendedto be limiting.

In this example, the end effector is maintained at a stationary positionrelative to the environment coordinate system ECS, and so the calculatedend effector path is controlled based on a null path having an effectivezero path length. Accordingly, the end effector 1313 is initiallyprovided coincident with the destination 1351, as shown in FIG. 13A.

As shown in FIG. 13B, the robot base undergoes unintentional movement,moving a distance shown by arrow 1361, so that the robot base is nowoffset from the original robot base coordinate system RBCS. This resultsin a modified robot base coordinate system RBCS′, which can be appliedto the robot arm kinematics as a shift in origin of the kinematics,causing the robot arm kinematics to be recalculated so that the endeffector is moved as shown in FIG. 13C, thereby aligning the endeffector with the destination 1351.

Accordingly, for an end effector path having a zero path length, thecalculated robot arm kinematics returns the end effector to the endeffector destination to thereby maintain the end effector static withinan environment coordinate system. In particular, as the origin of thekinematic chain of the robot arm dynamically shifts in the environmentcoordinate system, the end effector destination is used to update theinverse kinematics (i.e. joint angles for each link of the robot arm)necessary for the end effector to remain static to thereby compensatefor the moving origin of the robot arm.

It will be appreciated that similar techniques can be applied whentraversing the end effector 1313 along a path and/or when moving therobot base 1311 and this will not therefore be described in furtherdetail. However, it will be appreciated that for an end effector pathhaving a non-zero path length, the calculated robot arm kinematicsreturn the end effector to the end effector path. In this regard, as theorigin of the kinematic chain of the robot arm shifts, the controlsystem determines the desired end effector position on the end effectorpath and calculates the inverse kinematics required to achieve thedesired end effector position on the path. In this example, the dynamicorigin of the kinematic chain of the robot arm and the end effectordestination (which may be a final destination or path point along theend effector path) are both expressed in the environment coordinatesystem which simplifies control of the system.

In one example, the control system determines an end effector positionand then calculates the end effector path using the end effectorposition, so that the end effector path extends from the end effectorposition to the end effector destination.

As mentioned above the end effector position is typically determinedusing robot arm kinematics, based on the robot base position in theenvironment coordinate system, allowing the end effector path to bedirectly calculated in the environment coordinate system ECS, andcontrol performed in the environment coordinate system ECS, by shiftingan origin of the robot arm kinematics based on movement of the robotbase.

In another example, the end effector destination (i.e. desired endeffector position) is determined in the environment coordinate systemand then a transformation is applied to transform the desired endeffector position into the robot base coordinate system RBCS. This isachievable since the origin of the robot base coordinate system RBCS ismeasured by the tracking system and expressed in environmentcoordinates. In this example, control could then be implemented in therobot base coordinate system RBCS by calculating the inverse kinematicsrequired to move the end effector to the desired end effector position(which may be a path point along the end effector path or a finaldestination).

In one example, the end effector position is the current position, butalternatively, the end effector position could be an expected positionwhen the robot base reaches the reference robot base position, in whichcase the end effector position can be determined by transforming acurrent end effector position based on the reference robot baseposition.

Typically the control system operates by calculating a robot basemovement based on the current robot base position and then modifies therobot arm kinematics using the robot base movement. The movement istypically movement from an initial or expected robot base position,based on a robot base path extending to the robot base referenceposition. As in the previous example, the reference robot base positioncan be based on a current robot base position, a predicted robot baseposition based on movement of the robot base from a current robot baseposition, a predicted robot base position based on movement of the robotbase along the robot base path, or an intended robot base position whenan end effector reaches the end effector destination.

As in the previous example, although reference has been made to positiononly, the techniques are applicable to position and orientation.Accordingly, the end effector destination typically includes an endeffector pose with the tracking system measuring a robot base pose andthe control system determining a current robot base pose using signalsfrom the tracking system and calculating the robot arm kinematics basedon the robot base pose. In this case, the control system can determinean end effector pose and calculate the end effector path extending fromthe end effector pose to the end effector destination. Thus it will beappreciated that the above described technique can correct forvariations in pose as well as adjusting for position only.

Whilst the above example has focused on scenarios in which the robotbase moves, it will be appreciated that this is not essential and thesame techniques can be implemented when the robot base is static and theenvironment is moving relative to the robot base. Additionally, whilstthe description focuses on correction of unintentional movement only, itwill be appreciated that the arrangement can also compensate forintentional movement of the robot base.

In one aspect a process for performing dynamic path planning isprovided, and an example of this will now be described with reference toFIG. 14.

In this example, the end effector path is recalculated as needed basedon movements in the robot base position. In order to achieve this, thecontrol system 130 acquires the end effector destination at step 1400.

At step 1410, a robot base position is determined by the control system130. An end effector path is then calculated at step 1420, with the pathextending from the end effector position to the end effectordestination. The path is typically calculated in the robot basecoordinate system RBCS, which is achieved by transforming the endeffector destination into the robot base coordinate system RBCS usingthe robot base position, although alternatively the path could becalculated in the environment coordinate system ECS.

At step 1430 robot control signals are generated with these beingapplied to the robot arm to cause the robot arm to move at step 1440.Steps 1410 to 1440 are then repeated as needed so that an end effectorpath is constantly recalculated based on a robot base position, forexample taking into account deviation of the robot base position from arobot base path, thereby moving the end effector towards thedestination.

A number of different example scenarios will now be described withreference to FIGS. 15A to 15F, which show an end effector 1513 that isattached to a robot arm 1512, which is in turn attached to a robot base(which is not shown for clarity). The following examples will illustratethe dynamic path planning mechanism operating in two dimensions only,but it will be appreciated that this can extend to six degrees offreedom, and reference to two dimensions only is not intended to belimiting.

In the example shown in FIG. 15A, the end effector path is of zerolength so that a static end effector position relative to theenvironment is maintained. Accordingly, the end effector 1513 isinitially aligned with the destination 1551. Unintentional movement ofthe robot base introduces an offset 1561 which results in a new path1562 being calculated at step 1430, which returns the end effector 1513to the destination 1551.

In the example at FIGS. 15C and 15D, the end effector 1513 is beingmoved along an end effector path 1555 to the destination 1551. In thisinstance, an unintentional movement results in an offset 1561 as the endeffector is moved along the path 1563. This causes a new path 1565 to becalculated returning the end effector towards the destination 1551.

A further example is shown in FIGS. 15E and 15F, which involves movingthe end effector along an end effector path 1555, and simultaneouslymoving the robot base along a robot base path 1553. In this instance,the reference robot base position is shown in dotted lines in FIG. 15E,so that the end effector path 1555 is initially calculated to bevertically down to the destination 1551 from the reference robot baseposition. The net path 1556 formed from a combination of the endeffector path 1555 and the robot base path 1553 results in end effectormovement from the current end effector position to the destination 1551.

In this instance as the robot base and end effector are moved along thenet path as shown at 1563 an unintentional movement arises as shown as1561. In this instance a new path 1565 is calculated from an updatedreference robot base position, which when combined with robot basemovement results in a new net path 1565.

It will be appreciated that whilst the above described techniquerequires that the path is constantly recalculated, which is generallycomputational more expensive than the previously described DSTarrangements, this can have benefits. For example, the path traversed bythe end effector tends to head in a more direct manner towards thedestination, which then can result in a reduced number of pathcorrections and/or a reduced path distance. Additionally oralternatively, by reducing the number of corrections required, thisavoids the end effector path oscillating around a target path to correctfor movement of the robot base, which can reduce the need for sharpchanges in direction, which can in turn help ensure that the path iswithin the constraints of the robot dynamics and can hence be moreeasily achieved.

As mentioned above, in one example, the end effector destination istypically defined relative to an environment coordinate system in whichcase the control system calculates a transformed end effectordestination by transforming the end effector destination from theenvironment coordinate system ECS to the robot base coordinate systemRBCS at least in part using the robot base position. An end effectorpath can then be calculated extending to the transformed end effectordestination in the robot base coordinate system. However alternativelythe path calculation can be performed in the environment coordinatesystem ECS.

In one example, the control system determines an end effector positionand then calculates the end effector path using the end effectorposition, so that the end effector path extends from the end effectorposition to the end effector destination. The end effector position istypically determined in a robot base coordinate system using robot armkinematics.

It will be appreciated that the current robot base position could takeinto account robot base movement along a robot base path. Accordingly,in this instance the end effector path would be calculated based on areference robot base position, to take into account movement of therobot base along a robot base path, with the end effector path beingcalculated based on a deviation of the robot base position from therobot base path.

As in previous examples, the robot base moves with a slower dynamicresponse, whilst the end effector moves with a faster dynamic response,so that movement of the end effector can be used to correct for movementof the robot base away from an expected robot base position.

Whilst the above has been described with reference to position only, itwill be appreciated that the techniques are also applicable to positionand orientation. Accordingly, in one example the end effectordestination includes an end effector pose and the tracking systemmeasures a robot base pose. In this example, the control systemdetermines a robot base pose using signals from the tracking system andcalculates an end effector path based on the current base pose. In oneparticular example the control system determines an end effector poserelative to the robot base coordinate system and determines a currentrobot base pose using signals from the tracking system using both ofthese to calculate the end effector path.

Whilst the above example has focused on scenarios in which the robotbase moves, it will be appreciated that this is not essential and thesame techniques can be implemented when the robot base is static and theenvironment is moving relative to the robot base.

In one example, the control system includes a computer numerical control(CNC) system. In this regard, the CNC system can be formed as astandalone module, implemented as software, firmware, hardware or acombination thereof. In this instance, additional functionality can becalculated by other modules. For example, the system may implement a DSTmodule, which interfaces with the CNC module, to allow the system to becontrolled. For example, the DST module can calculate a correction orrobot arm kinematic origin shift, providing this to the CNC module toallow the robot arm to be controlled.

Throughout the above examples, and particularly when implementing DST,the steps are repeated to constantly update or correct for movement ofthe robot base. This is typically repeated for processing cycles of thecontrol system, and in particular consecutive processing cycles of thecontrol system. Thus, a new correction, robot arm kinematic origin shiftor new path can be calculated for each clock cycle of the controlsystem. In a further example, this is also performed based on a refreshrate of the tracking system, so that a new correction, etc, iscalculated each time the tracking system updates the robot baseposition. It will be appreciated from this, in one preferred example,the processing cycle of the control system and refresh rate of thetracking system have the same frequency, and even more preferably aretime synchronised.

The control signals are typically generated taking into account an endeffector velocity profile, robot dynamics and/or robot kinematics. Thisis performed to ensure that the robot arm is able to perform thenecessary motion. For example, a calculated end effector path couldexceed the capabilities of the robot arm, for example requiring a changein movement that is not feasible, or requiring movement at a rate thatcannot be practically achieved. In this instance, the path can berecalculated to ensure it can be executed.

In one example, this can be achieved by performing a movement thatcorresponds to the original planned movement, but which is limited inmagnitude to a feasible movement. In this instance, if further movementis required, this can be implemented in successive processing cycles.

An example of an overall control approach in which DST is performedusing dynamic compensation will now be described with reference to FIGS.16A to 16C. For the purpose of this example, it is assumed that thesystem is similar to that described above with respect to FIGS. 1B and1C, with the robot arm being mounted on a boom.

In this example, a robot base path is retrieved at step 1600. It will beappreciated that this can involve calculating a robot base path, forexample using the process described above with respect to FIG. 6.

At step 1602 tracking system signals are acquired with these being usedto determine a current robot base pose at step 1604. In particular, thiswould be calculated based on a tracking target pose, and transformedinto a current robot base pose using a geometrical transformation. Aspreviously described, in a preferred arrangement, the robot base pose ispreferably a virtual robot base pose, which is physically offset fromthe robot base, and aligned with the end effector.

At step 1606 it is determined if an interaction window is reached and ifnot the process moves on to step 1630. Otherwise assuming an interactionwindow has been reached a next step is selected at step 1608, with anend effector path being calculated and/or retrieved at step 1610, forexample using steps 1000 to 1030 of FIG. 10.

At step 1612 it is determined if stabilisation is required and if not,for example if the step involves retrieving an object from a deliverymechanism mounted on the robot base, the process proceeds to step 1624.

Otherwise, at step 1614, a robot base pose deviation is calculated basedon a deviation between a current robot base pose and expected robot basepose, as calculated from the robot base path. A scaling factor is thendetermined at step 1616, based on a proximity of the end effector to theend effector destination. At step 1618, the robot base deviation is usedto calculate a correction in the form of a vector including offsets foreach of six degrees of freedom, and representing the offset of the robotbase pose from the expected robot base pose. The correction is thenscaled based on the scaling factor.

A robot kinematic transform is calculated using the end effector pathand the scaled correction at step 1620, with this being assessed toensure dynamics are feasible at step 1622. In this regard, thecorrection may require that the robot arm undergo a movement whichexceeds the robot arm's capabilities, for example requiring a movementthat is too rapid. If the movement is not feasible, this can berecalculated or modified, for example by limiting the resultingmagnitude of the correction based on the robot arm dynamics. In oneexample, this is achieved by returning to step 1618, to recalculate thecorrection. However, this is not essential and in one example, thecontrol signals could be generated at step 1624 based on the robot armdynamics to simply implement the correction to the maximum degreepossible before the next processing cycle of the control system. Thus,if the correction requires end effector movement of 10 mm, but only a 5mm movement can be achieved prior to the next processing cycleimplemented by the controller, then the 5 mm movement would beimplemented.

At this point, the control system 130 can determine if the interactionis proceeding on schedule at step 1626, and if not the control system130 modifies the boom speed at step 1628, for example to slow downmovement of the boom. Whether or not the boom speed is modified, theresulting boom control signals are generated by the control system 130at step 1630.

Control signals are then applied to the respective actuators at step1632, to thereby move the boom and end effector. Tracking system signalsare acquired at step 1634, with this being used to determine a currentbase pose, following movement of the end effector and robot base, atstep 1636.

At step 1638, an assessment is made of whether the step is completed andif not the process returns to step 1612 to again determine ifstabilisation is required. Otherwise it is determined if all steps arecomplete at step 1640, with the process returning to step 1608 to selecta next step if not. Otherwise the process returns to 1606 to determinewhether a next interaction window has been reached.

It will be appreciated that by following the above described sequence,this allows the boom to be progressively moved along the boom path withinteractions being performed by performing sequences of steps, with eachstep involving the determination of an end effector path with the endeffector being moved along the end effector path to a destination.

Whilst the example of FIGS. 16A to 16C focus on the use of dynamiccompensation, it will be appreciated that similar approaches can be usedfor both dynamic coordinate system and dynamic path planning approachesto DST.

In one aspect a backup tracking process is provided, and an example ofthis will now be described with reference to FIG. 17.

In particular, the back-up tracking process is utilised in case thetracking system 120 fails. In this instance, the apparatus typicallyincludes a first tracking system similar to the tracking system 120described above, which measures the robot base position relative to theenvironment coordinate system ECS. A second tracking system is alsoprovided, which measures movement of the robot base, for example usingan Inertial Measurement Unit (IMU) 226 mounted on the robot base 111,which can communicate with the control system 130 via a respective IMUcontroller or processor. Such IMUs are well known and will not thereforebe described in any detail.

In this arrangement, the first tracking system is typically usedexclusively when functioning correctly, with the second tracking systembeing used as a back-up in the event that the first tracking systemfails. In this regard, failure may arise for any one of number ofreasons and could include a communications failure, processing failure,or could include occlusion of a tracking beam, such as a laser beam, inthe case of a laser tracking system.

In this process, at step 1700 the control system 130 receives signalsfrom the first tracking system, with these being used to detect failureat step 1710. This can be achieved in any suitable manner depending onthe nature of the failure and examples of this will be described in moredetail below.

If the first tracking system has not failed, the control system 130calculates the robot base position and/or pose at step 1720, with therobot base and end effector being optionally moved at steps 1730 and1740. Following this the process returns to step 1700, allowing thisprocess to be repeated. Thus, it will be appreciated in this instancethat if the first tracking system has not failed, then operation issubstantially as previously described.

However, in the event that tracking system failure is detected at step1710, signals from the second tracking system are acquired by thecontrol system 130 at step 1750, with these being used to determine arobot base position and/or pose at step 1760. In practice the signalsfrom the second tracking system are typically movement signalsindicative of movement of the robot base, with these being used togetherwith a last known location of the robot base, to determine the currentrobot base position.

At step 1770, the robot arm is optionally moved, depending on whethermovement is required to follow a robot base path. In the event thatmovement occurs, this is typically at a reduced speed below that of theoriginal robot base path velocity profile. Similarly, the end effectorcould be moved at step 1780, by moving the robot arm, with this againbeing performed at a reduced speed, compared to an end effector pathvelocity profile.

Following this the process returns to step 1700 with the control system130 attempting to determine signals from the first tracking system todetermine if this is functioning correctly, allowing the process to berepeated.

Accordingly, the above described system uses a first absolute positiontracking system but reverts to use of a second movement tracking system,such as an inertial guidance system, in the event that the absoluteposition tracking system fails. As such inertial systems are typicallynot as accurate and are subject to drift over time, it is typical tomove the robot base and/or robot arm more slowly to decrease risks ofcollision, and allowing the inertial to operate as accurately aspossible.

An example of the process for detecting failure will now be describedwith reference to FIG. 18.

In this example, at step 1800 the control system 130 attempts to acquiresignals from the first tracking system. If signals cannot be acquired,then a failure is detected at step 1810, and the process moves on tostep 1870. If signals are detected, these are assessed to determine ifthe signals are error signals at step 1820, if so a failure is detectedand the process proceeds to step 1870.

Otherwise the control system moves on to determine a robot base positionat step 1830. This is then compared to a previous robot base position todetermine if a change in position exceeds a threshold, corresponding toa viable amount of movement. For example, if the degree of movementsince the last position measurement exceeds the threshold, this islikely to indicate that at least one of the measurements is inaccurateand accordingly, a failure is detected at step 1870. Otherwise a failureis not detected, and the first tracking system can be used to determinethe position of the robot base.

In the event of failure of the first tracking system, the control system130 typically progressively reduces a robot base speed and haltsmovement of the robot base after a predetermined time period. Similarlythe control system typically progressively reduces the end effectorspeed and halts movement of the end effector after a predetermined timeperiod. Thus, the speed of the robot arm and robot base can be reducedprogressively over subsequent processing cycle iterations, so that therobot arm and/or robot base stop after a set period of time, to therebyfurther prevent any collision. This can be achieved in any suitablemanner, but typically involves scaling the end effector path velocityprofile and/or robot base path velocity profile. In the event that thefirst tracking system commences correct operation again, the speeds canbe progressively increased over subsequent processing iterations, tothereby gradually return the end effector and robot base to theirintended velocities, thereby avoiding sharp transitions in velocity,which could in turn induce vibrations in the robot actuator, leading tounintentional movement of the robot base.

In addition to using signals from the second tracking system to controlthe robot arm and/or robot base actuator, the control system can alsouse signals from the second tracking system to control the firsttracking system in an attempt to restore operation of the first trackingsystem. For example, if the tracking system operates by mutual positionrecognition of the tracking head and target, these can becomeunsynchronized should robot base move more than a set distance while thefirst tracking system is not operating. Accordingly, signals from theinertial sensing system can be used to guide the tracking head andtarget, allowing contact to be re-established without necessarilyrequiring that the robot arm is halted.

A further specific example will now be described. In particular, in thisexample, the control systems and methods of the invention have beendeveloped by the inventor in connection with an automated brick layingmachine. For a more detailed description of the brick laying machine,reference is made to the patent specification titled “Brick/Block LayingMachine Incorporated in a Vehicle” which is the subject of internationalpatent application PCT/AU2017/050731, the contents of which areincorporated herein by cross-reference.

An example of the automated brick laying machine is shown in FIGS. 19 to25.

In this example, the automated brick laying machine 1911 is built arounda vehicle in the form of a truck 1913 and has a base supporting atelescoping articulated boom assembly indicated generally at 1915,comprising long telescopic boom 1917 and telescopic stick 1919. Mountedto a remote end 1921 of the stick 1919 is an end effector in the form ofa laying head 1923 that supports a six axis robot arm 1925 that moves afurther end effector 1927 to manipulate the bricks 1929. The robot arm1925 has a robot base 1931, and mounted above the robot base 1931 is afirst target in the form of a six degree of freedom (6 DOF) high datarate position sensor 1933, that provides 6 DOF position coordinates,relative to a fixed ground reference 1935, to a control system. Mountedon the end of the robot arm 1925 immediately above the end effector 1927is an optional second target in the form of a 6 degree of freedom (6DOF) high data rate position sensor 1937, which provides 6 DOF positioncoordinates, relative to the fixed ground reference 1935, to the controlsystem. It will however, be appreciated that the end effector positioncould be determined based on the robot base position and the robot armkinematics, thereby obviating the need for the second position sensor1937.

The head 1923 is supported at the remote end of the stick assembly 1919(remote end of the boom 1915) about a pivoting horizontal axis 1938(horizontal with reference to the state of the vehicle 1913, assumingthe vehicle is stabilised level, absent any torsion).

In a general embodiment, the vehicle 1913 supports a boom 1915 whichsupports a robotic arm 1925 that supports an end effector 1927. The head1923 may optionally be omitted between the boom 1915 and the robot arm1925, but given the tasks to be performed by the end effector 1927,particularly the application of adhesive in a brick laying application,it is more practical to include the head 1923.

The vehicle 1913 may be parked stationary or jacked up on support legs1939. As an alternative, the vehicle 1913 may be programmed with a firstCNC channel to move, or may be manually driven, along a path. In thiscase a further third target in the form of a 6 degree of freedom (6 DOF)high data rate position sensor 1941 may be provided, that also provides6 DOF position coordinates, relative to the fixed ground reference 1935,to the control system. It will however, be appreciated that the vehicleposition could be determined based on the robot base position and theboom kinematics, thereby obviating the need for the position sensor1941. Where the vehicle traverses a path in this manner, there may needto be multiple fixed ground references of the same type of the fixedground reference 1935. Alternatively, in another embodiment, a low datarate and low accuracy position sensor such as GPS could be utilised, buthigh data rate is preferred.

For faster data handling it may be desirable to have multiple groundreferences 1935 a, 1935 b, 1935 c, each dedicated to their respectivesensor 1933, 1937 and 1941, as illustrated in FIG. 20.

The boom 1915 is programmed with a second CNC channel to move the TCP ofits end effector (located at the tip) of the boom to the requiredcoordinates.

The robot arm 1925 is programmed with a third CNC channel to move theTCP of its end effector 1927 to conduct tasks.

Optionally the end effector 1927 may include a fine dynamic compensationmechanism for very accurate work. Such a system may include a galvomirror to be used with a high power laser for laser cutting, engravingor 3D additive laser melting manufacture. The end effector is programmedwith a fourth CNC channel to move the TCP of the fine dynamiccompensation mechanism.

Referring to FIG. 22, detail of one embodiment is shown. A controlsystem is provided for the boom 1915 supported from a boom base in theform of the truck 1913. The boom 1915 has the head 1923 mounted about ahorizontal pivot axis 1938 at the remote end of the stick assembly 1919.The robot arm 1925 is mounted by the robot base 1931 to the head 1923.The end effector 1927 which comprises a gripper to pick up bricks ismounted for pitch roll and yaw movement to the end of the robot arm1927.

The control system includes a boom controller interfaced with a boomactuator in the form of hydraulic rams 1945 and 1947 (and a rotatingmechanism within the truck body—not shown) to move the boom 1915relative to the vehicle 1913 by to position the head 1923 and hence therobot base 1931 to a programmed location. The control system alsoincludes a robot arm controller interfaced with a robot arm actuator toposition said end effector at a programmed position and orientation. Thetracker system has fixed ground reference 1935 a to track the positionof the first target 1933 located by an offset proximal to the robot base1931. The tracker system has fixed ground reference 1935 b to track theposition and orientation of one of two second targets 1949 (whichever isvisible) located with a TCP offset from the TCP of the end effector1927. The tracker system tracks the position of the first target 1933and feeds data to said boom controller to operate said boom actuatorwith a slow dynamic response to dynamically position said first target1933 close to said offset to position said robot base 1931 close to saidprogrammed location, so that the end effector 1927 is within range ofthe position in which it is required to perform work. Since the targets1949 move with the end effector 1927, and the end effector can move withsix degrees of freedom, and the tracker system tracks both the positionand orientation of said second target with six degrees of freedom andfeeds data to the robot arm controller to operate said robot armactuator (including the end effector) with a fast dynamic response todynamically position and orientate said second target to said TCP offsetfrom said programmed position and orientation.

The control system may controllably switch control of the robot armcontroller between a first state where the robot arm controller isresponsive to positioning feedback data derived from the tracker system,and a second state where pre-calibrated positioning data referenced tothe robot base (and hence the remote end of the boom) is relied on. Themovement at the end effector 1927 relative to the robot base 1931 isrepresented by trace 2351 in FIG. 23, which shows deviations due todynamic structural effects on the boom, wind deflection or vehiclemovement, and the second state position for the robot arm is indicatedat 2353. When switched between the first state and the second state,said robot arm controller controls movement of the robot arm to damp orsmooth movement of the robot arm, through the transition between thefirst state and the second state, indicated by trace 2355, to avoidsudden movement of the robot arm and said end effector. Such suddenmovement could feed back to the boom, causing the boom to undergoreactive movement.

The switching between first and second states deals with applicationsthat require the end effector to alternately be controlled relative tothe machine structure and then the ground, for example to pick up abrick from part of the machine and then to lay a brick on a wallrelative to the ground.

FIG. 24 shows the end effector 1927 picking up a brick from the end ofthe boom. In this configuration the control system is in the secondstate and the tracker system need only track the first target 1933. FIG.25 shows the end effector 1927 about to lay the brick. In thisconfiguration the control system is in the first state, and the trackersystem must track the first target 1933 and the second target 1937. Thecontrol system transitions from the second state to the first state andvice versa in a slow manner, over a period of about a second, to dampthe movement of the end effector.

If the compensation was turned on or off immediately, the pose of thecompensating robot would have to change instantly, giving very largeforces and disturbance to the boom. To overcome this problem, it isnecessary for the compensation to be transitioned on or off or damped sothat the amount of compensation is gradually increased or decreased tothe required amount over a period of time, typically 0.2 to 0.5 seconds(or up to 10 seconds for large machines, or perhaps as low as in theorder of milliseconds, up to 0.1 seconds for small machines). With adynamic base coordinate system it is necessary to achieve thetransitioning effect by moving the base coordinate system from itsprogrammed position to the actual position over a period of time. It isimportant to check that the amount of compensation that will be appliedis within the working range of the compensation robot.

This is done by checking that the pose of the robot will be within theworking envelope. (If the calculated amount of compensation to beapplied would move the end effector beyond its working range, or exceedthe robot arm dynamic limits of jerk, acceleration, or velocity), if theactual position and orientation of the dynamic base coordinate systemwould place the robot in a pose beyond its working range of axis travelor the TCP outside of the working envelope of the robot arm, or exceedthe end effectors dynamic limits of jerk, acceleration, or velocity theamount of shift of the base dynamic coordinate system from theprogrammed location to the actual location (or the application of thecompensation amount), may be scaled back, or motion may be held untilthe system is returned to within its working range and/or a warning canbe issued within the controller.

Dynamic compensation transitioning works by, incrementing ifcompensation is turning on, or decrementing if compensation is turningoff, a transition factor between a value of 0 and 1, so that it S curveramps over the desired period of time, then, for each control cycle:

-   -   Measure the actual 6dof coordinates of the tip tracker.        Calculate the 6DOF coordinates of the actual coordinate system        of the base of the fine robot    -   If the transition factor is 1, then use the actual coordinate        system of the base of the fine robot as the dynamic coordinate        system.    -   If the transition factor is not 1 then:    -   Determine the programmed position of the coordinate system of        the base of the fine robot by considering the programmed        position of the boom tip and adding the kinematic transformation        to the base of the fine robot.    -   If the transition factor is 0, then use the programmed position        of the coordinate system as the dynamic coordinate system.    -   If the transition factor is between 0 and 1 then:    -   Calculate a 6DOF delta vector from the programmed to the actual        coordinate system of the base of the fine robot.    -   Scale the 6DOF vector by the transition factor to give a scaled        vector    -   Add the scaled vector to the programmed position of the        coordinate system to give the dynamic coordinate system.    -   Check the pose and dynamics to ensure that the fine robot is        within its working range. Go to warning, hold or scaling        algorithms.    -   If the transition factor is less than 1, increment the        transition factor, preferably using an S curve formula.

Preferably said machine includes a tracker component mounted to saidhead, wherein said head has said robotic arm assembly with said endeffector and said machine uses a tracker system to measure the positionand orientation of the tracker component and uses said measurement tocalculate the position and orientation of a base coordinate system forsaid robotic arm assembly. The robot arm end effector TCP is programmedto do tasks in either a coordinate system fixed to the head (equivalentto the robot base coordinate system RBCS above), or in a coordinatesystem fixed to a workpiece, fixed to the ground (equivalent to theenvironment coordinate system ECS above). The programming can shiftbetween the head coordinate system or the workpiece coordinate system,which in one example is performed by transitioning, which will beexplained below.

Transitioning to the dynamic base coordinate system involves moving thedynamic base coordinate system from a theoretical perfect position andorientation to an actual position and orientation (obtained by ameasurement of the position and orientation of a tracker component fixedto the head), in a gradual and controlled way.

Transitioning from the dynamic base coordinate system involves movingthe dynamic base coordinate system from an actual position andorientation (obtained by a measurement of the position and orientationof a tracker component fixed to the head), to the programmed (ie atheoretical) perfect position and orientation in a gradual andcontrolled way.

The most elegant mathematical approach to the arrangement is to have theboom TCP, tip tracker centre point and the dynamic coordinate system ofthe base of the robot arm coincident and aligned. In this way thekinematic transform set up in the boom CNC channel has its TCPcoincident with the tip tracker centre point. The kinematic transform ofthe robot arm CNC channel has its dynamic base coordinate systemcoincident with the tip tracker.

Those skilled in the art will appreciate that the boom TCP could be atposition different to the head base dynamic coordinate system anddifferent to the tip tracker centre point and mathematical transformscan be used to calculate the theoretical perfect position of the robotarm base dynamic coordinate system. This is a more complicated and lesselegant solution than that outlined above with coincident boom TCP, tiptracker CP and robot arm base dynamic coordinate system.

The control system uses a dynamic coordinate system offset or aplurality of dynamic coordinate system offsets to shift the basecoordinate system of the robot arm in real time in the ground coordinatesystem. The control system then uses a kinematic transformation tocalculate the required joint positions (angular or linear joints) toposition the end effector at the programmed position in the groundcoordinate system, rather than in the robot base coordinate system.

For large area tasks it may be necessary to move the vehicle relative tothe ground. The vehicle movement relative to the ground may beautomatically controlled or may be manually controlled withinpre-calculated guidelines. In any case the location of the machine baseis guided by either wheels or tracks, chains or rails or legs and feetand may not be very accurate. In this case, a multi stage control systemis used, the first stage approximately positions the vehicle, the secondstage positions a boom to a desired tip location and corrects at a slowrate any errors due to vehicle position and orientation and boomdeflection and a third stage measures the position and orientation of athird stage robot arm base coordinate system and then preciselypositions and compensates to stabilise and guide an end effectorrelative to the ground coordinate system. The number of stages ofmeasurement and control may be extended to any plurality of controlsystems, dynamic coordinate systems and measurement systems. It isimportant for stability that the bandwidth of the control and themechanical response speed of the motion systems increases from vehicleto end effector.

In some situations, it is necessary to stabilise the end effectorrelative to a moving object rather than the ground. Provided therelative position of the vehicle coordinate system and the tip trackercoordinate system is measured relative to the moving object coordinatesystem (or vis versa), compared to the vehicle, the moving object may beregarded as analogous to the ground, except that it is not an inertiallyfixed coordinate system. In this case, preferably a measurement to aninertially fixed coordinate system (eg earth or an INS, albeit a slowlyrotating coordinate system) is also made to enable motion dynamic limitsto be observed.

The control system can be used for tasks such as automated brick laying,precision mining, machining, robot assembly, painting and 3D printing.It has particular application for automated trenching for infrastructurepipelines, railway and road construction, automated pipe laying and forbuilding long walls such as freeway sound wall.

The invention can be applied to airborne or seaborne equipment forapplications such as dredging, seawall construction, oilfield and windturbine maintenance, crew transfer, ship to ship transfer or air to airtransfer or refueling or helicopter powerline maintenance or helicopterlogging.

The invention applies to multiple kinematic chains and multiple dynamiccoordinate systems. The invention is particularly useful to stabilise,relative to the ground, an end effector, attached to a boom that is on amoving machine. When a machine moves, the acceleration of the machineimparts a dynamic force to the boom and the boom starts to oscillate atits natural frequency. Provided the compensating robot at the end of theboom has an amplitude larger than the amplitude of the boom motion, anda response much faster than the natural frequency of the boom (andvehicle), the compensating robot can correct for the boom motion due tobounce from the vehicle travel. The compensating robot does not havemuch range of motion so it is necessary to also correct the pose of theboom to keep the compensating robot within its available range ofmotion.

The actuation of the compensating robot imparts dynamic forces to theboom, which in turn further excite the boom. To minimise jerky motion ofthe boom, it is desirable for the boom to be rigid and free ofmechanical play and backlash.

It is desirable for the (optional) moving vehicle to travel smoothly, soit is desirable for the ground it moves over to be graded and it isdesirable for the vehicle to have suspension. Ideally the suspension isself-levelling. Optionally the vehicle may be fitted with a controllableblade so that it levels the ground before it drives over it. Optionallythe end effector may be a blade or bucket and the machine may grade andlevel its own path prior to moving on to it.

To minimise jerky motion of the machine and the boom the control systemof the vehicle of the machine is used to carefully control the motion.Preferably a mode of operation can be set when stabilised end effectoroperation is desired. The vehicle and boom motion is preferably jerk,acceleration and velocity limited. In an electro hydraulic controlsystem, the electrical pilot system is controlled to limit the availablecontrol input. In a servo electric system, the servo dynamics arelimited, preferably by the CNC channel and axis configuration.Preferably full CNC path planning is utilised rather than set point orpoint to point motion control. A full CNC path planner calculates pathpoints for every control cycle (typically every ms). Preferably itcalculates a path to optimise position, velocity, acceleration and jerk.A point to point control simply changes the set point to the desired endpoint, so that a large control feedback error value is created and thefeedback control loop commands the motion to close the error.

The measurement of the vehicle position and orientation may be backcalculated from the measurement of the 6DOF tip tracker (using theinverse kinematic chain of the boom, which of course will not take intoaccount deflection or vibration of the boom, unless it was measured forexample by accelerometers, but would typically have the tip trackermotion heavily filtered to smooth the vibration component of themotion). Preferably the vehicle position and orientation is provided bya position tracking device fitted to the vehicle of the machine, or apart of the machine near the vehicle, such as the cab on an excavator.The vehicle tracking device may have a relatively low data rate and lowaccuracy such as GPS or total station target but the best performancewould be achieved with an accurate sensor system such as a laser trackerand smart track sensor.

The motion of the boom is controlled at a bandwidth significantly lessthan its natural frequency (1% to 10% or 10% to 20% or 30% to 50% or 50%to 99%) so as to slowly compensate for boom motion errors and deflectionand base motion errors or movement. The controlled motion of the boomaims to correct the position of the tip of the boom, but not necessarilythe boom tip orientation. The boom control and response may have abandwidth of 0.1 to 1 Hz, or 1 Hz to 10 Hz or 10 Hz to 30 Hz. The endeffector compensating robot must have a high natural frequency (relativeto the boom and base) and a fast dynamic response. The compensatingrobot compensates and stabilises in 6 DOF. The measurement system of thetip tracker must have a high data rate, preferably at the same servoloop control rate as the end effector control system, a minimum of 250Hz and preferably 1000 Hz or greater (perhaps 10 kHz). If the data rateis significantly lower, the dynamic coordinate system position andorientation (ultimately resulting in a compensation input) has stepchanges that may induce structural vibration as the system responds tothe actuator force inputs. If the step changes are filtered to provide asmooth change, a delay and motion lag is introduced and the end effectorposition is not accurate and may oscillate relative to the ground.

A chain of dynamic coordinate systems and a machine with a chain ofcompensating booms and robotic compensating end effectors is useful inmany applications requiring fine position and motion control over alarge working volume.

Some example applications are given below:

Ship Transfer

Ship to ship, or ship to oil rig, or ship to gas rig, or ship to windturbine, transfer of goods, liquids or personnel, is a potentialapplication for the control system of the invention. It is known tostabilise a vessel for position holding. It is also known to rollstabilise a vessel with gyros or thrusters. It is known to yaw stabilisea vessel with thrusters. It is also known to provide heave, pitch, rolland yaw compensation to working devices such as booms.

However, it is known that for long booms in heavy sea states theexisting methods of compensation have limitations. A coarse boompositioning and fine end effector positioning, or even additional stagesof fine positioning would enable safer transfer, hook up, disconnectionand operations in larger sea states and rougher weather.

For example FIGS. 27 and 28 show a boom 2715 mounted on a FPSO 2759(Floating, Production, Storage and Offloading vessel) transferring LNGto a LNG tanker 2757. The boom 2715 has a fine positioning arm 2725which can approach close to or connect to the tanker. Trackers 2735 a,2735 b measure the relative position of the boom tip 2733 and the tip2737 of the fine positioning arm. If the fine positioning arm isconnected or engaged with the tanker 2757, the control system isswitched to a passive mode (ie no active control) so that the finepositioning arm now acts as a suspension system to absorb relativemovement between the boom tip and the tanker.

Referring to FIG. 29, a platform stabilised in six degrees of freedom bya Stewart Platform 2971 on the deck of a supply vessel 2963, relative toan oil or gas rig 2965 or FPSO (Floating Production Storage andOffloading vessel), as illustrated, would enable much safer transfer ofgoods and personnel using the existing cranes on the rig or FPSO.Tracker 2967 on the rig 2965 tracks target 2969 on the vessel 2963,while tracker 2935 a on the vessel tracks target 2933 at the end of theboom 2915. This data is fed to the control system located with the baseof the boom on the rig via radio link as necessary to control the boom2915 and end effector 2927 as discussed, and may also be fed back toassist to control the Stewart Platform 2971 on the deck of the vessel2963. This provides a particularly significant operating advantage forhandling large and expensive items. Currently when sea state reaches alimit, transfers have to be stopped.

This could have great benefit for petrochemical, renewable energy andmilitary operators (and others) that require or desire to transferthings from vessel to vessel or vessel to fixed objects in all weatherconditions.

Long Building

Long structures such as road freeway sound walls can be built by thebrick laying machine, as shown in FIG. 26. With traditional arrangementsit is necessary to build from one location, then reposition periodicallyand build from the next stationary location. It would be advantageous tobe able to build from a creeping machine. This would reduce lost time toreposition and would enable a smaller more compact machine with ashorter boom. A track mounted machine 2613 with a short boom 2615 wouldbe ideal. Multiple fixed ground references 2635 are provided tofacilitate this.

Long Trenching

Long trenches for infrastructure such as underground pipe lines andunderground cables can be dug with known continuous trenching machines(such as made by Ditch Witch or Vermeer) or for larger cross sectiontrenches with excavators (such as made by Caterpillar, Volvo, JohnDeere, Komatsu and others). For many applications the precise grade andlocation of the trench and pipe is important, such as for sewerage pipe.For many applications knowing the precise position is important, such asin cities to avoid damaging existing infrastructure such as pipes,cables, foundations and underground train and road tunnels. Currentsystems allow some control of the digging and provide feedback to theoperator of dig depth or bucket position. In current system the base ofthe machine (the tracks) must be stationary.

The dynamic control system described allows precision digging to atolerance that cannot be currently achieved by other methods.Further-more it allows pre-programmed digging for completely autonomousoperation. Further-more it allows precision digging from a continuouslymoving machine such as a tracked excavator creeping along the path ofthe proposed trench.

Ground Contouring

It is known to use graders, bulldozers, loaders, gradall or automatedscreeding machines to smooth earth or concrete surfaces with blades orbuckets. The inherent design of the machine will achieve a flattersurface than it moves over because the geometry of the machine providesa smoothing action. It is known that a more accurate and faster resultcan be achieved with automatic control to maintain the bucket or bladeon a predefined level, grade or contour. The blade or bucket is moved upor down or tilted about a roll axis automatically to maintain a laserplane level or grade or to match a contour referenced by GPS or totalstation measurements. These known control systems have a low bandwidthand the machine achieves an accurate result because the inherent designof the machine will achieve a flatter surface than it drives over, evenwithout machine guidance.

The present invention allows more complex machine arrangements such as a(modified) excavator, to be fitted with a multi axis controlled blade orbucket to achieve very complex earthmoving tasks in a completelyprogrammable way.

Mining

It is known to use autonomous trucks for mining.

Excavators and face shovels are currently operated by machine operators.This technology enables autonomous control of excavators and faceshovels by pre-programming the base movement (track base) and the digprogram in mine coordinates.

Dredging

Excavators mounted on barges are used for dredging. Dredged channeldepth, width, profile and location is extremely important for shippingsafety. Dredging is expensive so it is advantageous to minimise theamount of spoil moved. The more accurate the dredging, the less spoilneeds to be removed.

The barges are floating so as the excavator moves, the barge pitches androlls and moves. Measuring the barge position and orientation in 6dof inreal time enables the bucket position to be precisely calculated (viaknown sensors that measure the pose of the excavator), or evencontrolled to a set of pre-programmed dig locations.

Elevated Work Platforms

It is known to use various kinds of elevated work platforms (EWP) suchas boom lifts or scissor lifts or vertical telescoping lifts made bymanufacturers such as JLG, Snorkel and Genie. It is known that very tallboom lifts sway with a large amplitude and make work difficult,dangerous or impossible. The sway is the limiting factor for the heightthat boom lifts can work at. It is known that driving the boom lift orEWP with the platform up excites sway and makes the platformuncomfortable or dangerous. The present invention provides means to makea stabilised platform so that the platform is stabilised relative to theground, or to a desired trajectory when the platform or EWP is moved.

Cable Suspended Robots

It is known to support a robot on a platform suspended by cables intension supported by an overhead gantry or towers (see PARSystems—Tensile Truss and Chernobyl Crane and demolition robot). Thecables can support high loads but the structure has low stiffness. Thelateral stiffness is very low. The accuracy of the positioning of therobot and end effector would be greatly improved by adding a trackingcomponent to the suspended platform to provide a 6DOF position of thebase of the robot arm. This would enable such a system to do accuratework, rather than the relatively inaccurate demolition work it ispresently employed to do.

Very Accurate Applications

Such a system may include a galvo mirror to be used with a high powerlaser for laser cutting, laser engraving or 3D additive laser meltingmanufacture.

It will be appreciated that a wide range of other uses are alsoenvisaged. For example, the system can be used to perform constructionof multi-story and/or high-rise buildings. In this regard, the robotbase can be supported by or remotely to the building duringconstruction, with the system being used to compensate for movement ofthe robot base relative to the building, which might arise from windloading of the building and/or the support system used to support therobot base.

The system could also be used with a wide range of additional vehiclesto those mentioned above, such as space vehicles. In this example, therobot base could be mounted on the space vehicle, allowing this to beused to perform an interaction with another vehicle, for example tofacilitate docking, satellite retrieval, or the like, or other objects,such as interaction with an asteroid or similar.

In one example, the system uses a cascading system of positioningdevices, measurement systems and control channels. In one embodiment, awide ranging inaccurate gross motion system guides a vehicle whichsupports a large area coarse positioning boom which then supports asmall dynamic compensation and fine positioning robot which then in turnsupports an even finer dynamic compensation and positioning mechanism.

In one example, the system describes dynamic coordinate systems andmethods of moving machines and stabilising end effectors. In preferredembodiments, methods of transitioning compensation on and off, ordamping transitioning are provided, so that the robot arm moving the endeffector may work alternately in a head coordinate system and a groundor work coordinate system.

It is advantageous to code a kinematic transformation as a stand-alonepiece of software. This means that the CNC kernel does not have to bemodified to accommodate different kinematic chains. By using a dynamiccoordinate system as the base of the end effector robot kinematic chain,the end effector can be programmed in a work coordinate system and allof the normal CNC coordinate shifts and transformations work, such asoffsets for work coordinates and coordinate system rotation.

With a dynamic coordinate system for the base of the kinematic chain ofthe robot arm the concept of a compensation amount is abstract. If thebase of the kinematic chain of the robot arm was at its programmedlocation there would be no compensation amount and the robot arm wouldbe in a first pose. If the base is at its actual location and the robotarm was in the first pose, the end effector would be at the wronglocation (and in the wrong orientation), the difference being thecompensation amount.

In one example, there is provided a control system for an arm supportedfrom an arm base, said arm having an end effector mounted therefrom,said end effector having a further arm supported by a further arm baseand said further arm having a further end effector mounted thereon, saidarm being moveable relative to said arm base by an arm controllerinterfaced with an arm actuator to position said end effector to aprogrammed location, said further arm being movable by a further armcontroller interfaced with a further arm actuator to position saidfurther end effector at a programmed position; said control systemhaving a tracker system to track the position of a first target locatedby an offset proximal to said further arm base or end effector, and totrack the position and orientation of a second target located with a TCPoffset from said further end effector; wherein said tracker systemtracks the position of said first target and feeds data to said armcontroller to operate said arm actuator with a slow dynamic response todynamically position said first target close to said offset to positionsaid further arm base close to said programmed location, and saidtracker system tracks the position and orientation of said second targetand feeds data to said further arm controller to operate said furtherarm actuator with a fast dynamic response to dynamically position andoptionally orientate said second target to said TCP offset from saidprogrammed position and optionally orientation. The TCP offset may bedefined by position and optionally orientation data. The differencebetween the slow dynamic response and the fast dynamic response isinversely proportional to the potential inertia of the arm and thefurther arm. Where the further arm is much smaller than the arm, thefurther arm will possess less potential inertia and may be moved with arelatively fast dynamic response.

In one example, said second target is located with said TCP offset fromsaid further end effector so as to move with movement and pose of saidfurther end effector. In this case the TCP offset is defined by positionand orientation data, and said tracker system measures the position andorientation of said second target.

By “close to” said programmed location, the further arm base is movedsufficiently close that the further end effector is within range of itsprogrammed task, i.e. the further arm can move the further end effectorto a position in order that the task the further end effector is toperform can be completed. By dynamically position and dynamicallyposition and orientate, it is to be understood that as the position ofthe further arm base varies due to deflection, its position (andorientation if applicable, see hereinafter) is constantly under reviewand adjusted by the arm actuator with slow dynamic response, and theposition and orientation of the further end effector is also constantlyunder review and adjusted by the further arm actuator with fast dynamicresponse.

In one example, said further arm base is mounted proximal to a remoteend of said arm, away from said arm base.

In one example, said further arm base and said first target is mountedon a head, mounted to the remote end of the arm.

In one example, said head is pivotally mounted to the remote end of thearm.

In one example, said head is pivotally mounted about a horizontal axisto the remote end of the arm.

In one example, said tracker system tracks the position and orientationof said first target, and feeds data to said arm controller to operatesaid arm actuator with a slow dynamic response to position and orientatesaid first target close to said offset to position said further arm baseclose to said programmed location.

Where the head is pivotally mounted to the remote end of the arm, thepoise of the head may be controlled by a separate controller to the armcontroller, in which case the arm controller need only operate the armactuator to position the first target along three orthogonal axes.However, control of the poise of the head may be integrated into the armcontroller, in which case the position and orientation of the firsttarget can be tracked.

Where the head is pivotally mounted to the remote end of the arm about amulti axis mechanism, the position and orientation of the first targetcan be tracked with six degrees of freedom. The position and orientationof the second target can be tracked with six degrees of freedom.

In one example, said tracker system includes separate target trackingdevices for said first target and said second target.

In one example, said further arm controller may be controllably switchedbetween a first state wherein said further arm controller is responsiveto positioning feedback data derived from said tracker system, to asecond state where pre-calibrated positioning data referenced to thefurther arm base (and hence the remote end of the arm) is relied on, andwhen switched between said first state and said second state, saidfurther arm controller controls movement of said further arm to dampenmovement of the further arm, to avoid sudden movement of said furtherarm and said further end effector. Such sudden movement could feed backto the arm, causing the arm to undergo reactive movement.

In one example, said arm base is provided with movement apparatus tomove said arm base relative to the ground. The movement apparatus may beselected from a wheeled conveyance, incorporating locomotion or not, orself-powered endless tracks. The movement apparatus may incorporateself-levelling to level the arm base.

In one example, said arm base is mounted on an active suspension system,and said arm base incorporates a third target for said tracker system,said active suspension system having a suspension controller interfacedwith a suspension actuator to control the position and orientation ofsaid arm base in response to data from said tracker system reading theposition and orientation of said third target.

Alternatively, said arm base is mounted to an object having largerinertia than said arm on an active suspension system, and said arm baseincorporates a third target for said tracker system; said activesuspension system having a suspension controller interfaced with asuspension actuator to control the position and orientation of said armbase relative to said object in response to data from said trackersystem reading the position and orientation of said third target, saidsuspension actuator to control the position of said arm base with aslower dynamic response than said arm controller operates said armactuator.

In another example, there is provided a control system for a boomsupported from a boom base, said boom having a robot arm mounted by arobot base therefrom, said robot arm having an end effector, said boombeing moveable relative to said boom base by a boom controllerinterfaced with a boom actuator to position said robot base to aprogrammed location, said robot arm being movable by a robot armcontroller interfaced with a robot arm actuator to position said endeffector at a programmed position and orientation; said control systemhaving a tracker system to track the position of a first target locatedby an offset proximal to said robot base, and to track the position andorientation of a second target located with a TCP offset from said endeffector TCP; wherein said tracker system tracks the position of saidfirst target and feeds data to said boom controller to operate said boomactuator with a slow dynamic response to dynamically position said firsttarget close to said offset to position said robot base close to saidprogrammed location, and said tracker system tracks the position andorientation of said second target and feeds data to said robot armcontroller to operate said robot arm actuator with a fast dynamicresponse to dynamically position and orientate said second target tosaid TCP offset from said programmed position and orientation. The TCPoffset may be defined by position and orientation data.

In one example, said second target is located with said TCP offset fromsaid end effector TCP so as to move with movement and pose of said endeffector.

By “close to” said programmed location, the robot base is movedsufficiently close that the end effector is within range of itsprogrammed task, i.e. the robot arm can move the end effector to aposition in order that the task the end effector is to perform can becompleted. By dynamically position and dynamically position andorientate, it is to be understood that as the position of the robot basevaries due to deflection, its position (and orientation if applicable,see hereinafter) is constantly under review and adjusted by the boomactuator with slow dynamic response, and the position and orientation ofthe end effector is also constantly under review and adjusted by therobot arm actuator with fast dynamic response.

In one example, said robot base is mounted proximal to a remote end ofsaid boom, away from said boom base.

In one example, said robot base and said first target is mounted on ahead, mounted to the remote end of the boom.

In one example, said head is pivotally mounted to the remote end of theboom.

In one example, said head is pivotally mounted about a horizontal axisto the remote end of the boom.

In one example, said tracker system tracks the position and orientationof said first target, and feeds data to said boom controller to operatesaid boom actuator with a slow dynamic response to position andorientate said first target close to said offset to position said robotbase close to said programmed location.

Where the head is pivotally mounted to the remote end of the boom, thepoise of the head may be controlled by a separate controller to the boomcontroller, in which case the boom controller need only operate the boomactuator to position the first target along three orthogonal axes.However, control of the poise of the head may be integrated into theboom controller, in which case the position and orientation of the firsttarget can be tracked.

Where the head is pivotally mounted to the remote end of the boom abouta multi axis mechanism, the position and orientation of the first targetcan be tracked with six degrees of freedom. The position and orientationof the second target can be tracked with six degrees of freedom.

In one example, said tracker system includes separate target trackingdevices for said first target and said second target.

In one example, said robot arm controller may be controllably switchedbetween a first state wherein said robot arm controller is responsive topositioning feedback data derived from said tracker system, to a secondstate where pre-calibrated positioning data referenced to the robot base(and hence the remote end of the boom) is relied on, and when switchedbetween said first state and said second state, said robot armcontroller controls movement of said robot arm to dampen movement of therobot arm, to avoid sudden movement of said robot arm and said endeffector. Such sudden movement could feed back to the boom, causing theboom to undergo reactive movement.

In one example, said boom base is provided with movement apparatus tomove said boom base relative to the ground. The movement apparatus maybe a vehicle selected from a wheeled conveyance, incorporatinglocomotion or not, or self-powered endless tracks. The movementapparatus may incorporate self-levelling to level the boom base. Suchself-levelling should move the boom base to stabilise the boom base andhence the boom, against changes of position and orientation of the boombase, brought about by undulations in the ground over which the vehicletraverses.

In one example, said boom base is mounted on an active suspensionsystem, and said boom base incorporates a third target for said trackersystem, said active suspension system having a suspension controllerinterfaced with a suspension actuator to control the position andorientation of said boom base in response to data from said trackersystem reading the position and orientation of said third target.

Alternatively, said boom base is mounted to an object having largerinertia than said boom on an active suspension system, and said boombase incorporates a third target for said tracker system; said activesuspension system having a suspension controller interfaced with asuspension actuator to control the position and orientation of said boombase relative to said object in response to data from said trackersystem reading the position and orientation of said third target, saidsuspension actuator to control the position of said boom base with afaster dynamic response than said boom controller operates said boomactuator.

The control system may include multiple tracker components at variouspositions on the machine so that a tracker (or multiple trackers) has orhave line(s) of sight to one or more tracker components supported by themachine.

In one example, the control system of the machine includes algorithms toevaluate line of sight so that the best line of sight, between trackerand tracker component, in a particular pose can be chosen. The criteriafor the best line of sight include, most accurate position andorientation solution (which may depend on the pose of the tracker or itssensor), field of view of the tracker or the sensor, distance to the endeffector (closer is better), maintaining line of sight at all timesduring a programmed path or a critical operation.

In one example, said machine includes a further tracker componentsupported on said robotic arm, or on said end effector, and said machineuses a further tracker system to measure the position of the furthertracker component and applies further compensating movement to therobotic arm assembly to correct for variance between programmed furthertracker component position and measured further tracker componentposition.

The boom base may be a vehicle which may include a tracker component ata position on the vehicle or a plurality of tracker components atvarious positions on the vehicle. The tracker component(s) may be usedto determine the position and orientation of the vehicle relative to aworkspace coordinate system. The tracker component(s) may be used todetermine the position and orientation of a vehicle for a movingvehicle. The tracker system may include multiple ground references totrack the tracker targets as the vehicle progresses along a path.

The arrangements described above can achieve a high degree of dynamicmotion quality and position tolerance over a large size of workspace.This results in smoother motion for end effectors located at the end oflong booms or towers or supported on long cable trusses. Thearrangements of the invention can smooth motion for an end effectorsupported by a long boom or tower supported by a moving vehicle.

Further details of the applicants technology are described in patentpublications and co-pending applications U.S. Pat. No. 8,166,727,PCT/AU2008/001274, PCT/AU2008/001275, PCT/AU2017/050731,PCT/AU2017/050730, PCT/AU2017/050728, PCT/AU2017/050739,PCT/AU2017/050738, PCT/AU2018/050698, AU2017902625, AU2017903310,AU2017903312, AU2017904002 and AU2017904110, the contents of which areincorporated herein by cross reference.

Throughout this specification and claims which follow, unless thecontext requires otherwise, the word “comprise”, and variations such as“comprises” or “comprising”, will be understood to imply the inclusionof a stated integer or group of integers or steps but not the exclusionof any other integer or group of integers. As used herein and unlessotherwise stated, the term “approximately” means±20%.

Persons skilled in the art will appreciate that numerous variations andmodifications will become apparent. All such variations andmodifications which become apparent to persons skilled in the art,should be considered to fall within the spirit and scope that theinvention broadly appearing before described.

The claims defining the invention are as follows: 1) A system forperforming interactions within a physical environment, the systemincluding: a) a robot base that undergoes movement relative to theenvironment; b) a robot arm mounted to the robot base, the robot armincluding an end effector mounted thereon; c) a tracking system thatmeasures a robot base position indicative of a position of the robotbase relative to the environment; and, d) a control system that: i)acquires an indication of an end effector destination; ii) determines arobot base position using signals from the tracking system; iii)calculates an end effector path extending to the end effectordestination at least in part using the robot base position; iv)generates robot control signals based on the end effector path; v)applies the robot control signals to the robot arm to cause the endeffector to be moved along the end effector path towards thedestination; and, vi) repeats steps (ii) to (vi) to move the endeffector towards the end effector destination. 2) A system according toclaim 1, wherein the end effector destination is defined relative to anenvironment coordinate system and the control system: a) calculates atransformed end effector destination by transforming the end effectordestination from the environment coordinate system to the robot basecoordinate system at least in part using the robot base position; and,b) calculates an end effector path extending to the transformed endeffector destination in the robot base coordinate system. 3) A systemaccording to claim 1 or claim 2, wherein the end effector destinationincludes an end effector pose, the tracking system measures a robot basepose and wherein the control system: a) determines a current robot basepose using signals from the tracking system; and b) calculates an endeffector path based on the current robot base pose. 4) A systemaccording to any one of the claims 1 to 3, wherein the control system:a) determines an end effector pose relative to the robot base coordinatesystem; b) determines a current robot base pose using signals from thetracking system; and, c) calculates the end effector path using thecurrent robot base pose. 5) A system according to any one of the claims1 to 4, wherein the control system: a) determines an end effectorposition; and, b) calculates the end effector path using the endeffector position. 6) A system according to claim 5, wherein the controlsystem determines the end effector position in a robot base coordinatesystem using robot arm kinematics. 7) A system according to any one ofthe claims 1 to 6, wherein the robot base moves with a slower dynamicresponse and the end effector moves with a faster dynamic response tocorrect for movement of the robot base away from an expected robot baseposition. 8) A system according to any one of the claims 1 to 7, whereinthe robot base is a movable robot base, and the system includes a robotbase actuator that moves the robot base relative to the environment. 9)A system according to claim 8, wherein the control system: a) calculatesa robot base path extending from a current robot base position at leastin part in accordance with an end effector destination; b) generatesrobot base control signals based on the robot base path; and, c) appliesthe robot base control signals to the robot base actuator to cause therobot base to be moved along the robot base path. 10) A system accordingto claim 9, wherein the robot base path is configured to allowcontinuous movement of the robot base along the robot base path inaccordance with a defined robot base path velocity profile. 11) A systemaccording to any one of the claims 1 to 10, wherein the control system:a) determines a virtual robot base position offset from the robot baseand defined at least partially in accordance with an end effectorposition; and, b) uses the virtual robot base position to at least oneof: i) calculate a robot base path; and, ii) generate robot baseactuator control signals. 12) A system according to claim 11, whereinthe virtual robot base position is coincident with a reference endeffector position, the reference end effector position being at leastone of: a) an operative position indicative of a position of the endeffector when performing an interaction in the environment; b) apre-operative position indicative of a position of the end effectorprior to commencing an interaction in the environment; and, c) a defaultposition indicative of a position of the end effector followingperforming an interaction in the environment. 13) A system according toclaim 11 or claim 12, wherein the tracking system measures a targetposition indicative of a position of a target mounted on the robot baseand the control system determines the virtual robot base position usingthe target position by transforming the target position to the virtualrobot base position. 14) A system according to any one of the claims 1to 13, wherein the control system: a) acquires an indication of aplurality of end effector destinations; b) determines a robot baseposition at least in part using signals from the tracking system; c)calculates a robot base path extending from the robot base position inaccordance with the end effector destinations, the robot base path beingconfigured to allow continuous movement of the robot base along therobot base path in accordance with a defined robot base path velocityprofile; d) generates robot base control signals based on the robot basepath; and, e) applies the robot base control signals to the robot baseactuator to cause the robot base to be moved along the robot base pathin accordance with the robot base path velocity profile. 15) A systemaccording to claim 14, wherein, at least one of: a) the robot base pathdoes not include any discontinuities; and, b) robot base path velocityprofile does not include any discontinuous velocity changes. 16) Asystem according to claim 14 or claim 15, wherein the control system: a)defines an interaction window; and, b) determines the robot base path atleast in part using the interaction window. 17) A system according toany one of the claims 1 to 16, wherein the control system: a) monitorsend effector interaction; and, b) selectively modifies the robot basecontrol signals to cause the robot base to move at a robot base velocitybelow the robot base path velocity profile, depending on results of themonitoring. 18) A system according to any one of the claims 1 to 17,wherein the robot base path includes an interaction window associatedwith each end effector destination, and wherein as the robot base entersan interaction window, the control system: a) controls the robot arm tocommence at least one of: i) interaction; and, ii) movement of the endeffector along an end effector path to the end effector destination;and, b) monitors interaction by determining if the interaction will becompleted by the time the robot base approaches an exit to aninteraction window; and, c) progressively reduces the robot basevelocity to ensure the interaction is completed by the time the robotbase reaches an exit to the interaction window. 19) A system accordingto any one of the claims 1 to 18, wherein the system includes: a) afirst tracking system that measures a robot base position indicative ofa position of the robot base relative to the environment; and, b) asecond tracking system that measures movement of the robot base, andwherein the control system: i) determines the robot base position atleast in part using signals from the first tracking system; and, ii) inthe event of failure of the first tracking system: (1) determines arobot base position using signals from the second tracking system; and,(2) controls the robot arm to move the end effector along the endeffector path at a reduced end effector speed. 20) A system according toclaim 19, wherein the system includes: a) a robot base; and, b) a robotbase actuator that moves the robot base relative to the environment, andwherein the control system uses the robot base position to at leastpartially control the robot base actuator to move the robot base along arobot base path, and wherein in the event of failure of the firsttracking system: i) determines the robot base position using signalsfrom the second tracking system; and, ii) controls the robot baseactuator to move the robot base along the robot base path at a reducedrobot base speed. 21) A system according to any one of the claims 1 to18, wherein the tracking system includes: a) a tracking base including atracker head having: i) a radiation source arranged to send a radiationbeam to a target; ii) a base sensor that senses reflected radiation;iii) head angle sensors that sense an orientation of the head; iv) abase tracking system that: (1) tracks a position of the target; and, (2)controls an orientation of the tracker head to follow the target; b) atarget including: i) a target sensor that senses the radiation beam; ii)target angle sensors that sense an orientation of the head; iii) atarget tracking system that: (1) tracks a position of the tracking base;and, (2) controls an orientation of the target to follow the trackerhead; and, c) a tracker processing system that determines a relativeposition of the tracker base and target in accordance with signals fromthe sensors. 22) A system according to any one of the claims 1 to 7,wherein the robot base is static and the environment is moving relativeto the robot base. 23) A system according to any one of the claims 1 to22, wherein the control system generates the robot control signalstaking into account at least one of: a) an end effector velocityprofile; b) robot dynamics; and, c) robot kinematics. 24) A systemaccording to any one of the claims 1 to 23, wherein the control systemincludes a computer numerical control system. 25) A system according toany one of the claims 1 to 24, wherein the control system at least oneof: a) repeats steps for processing cycles of the control system; b)repeats steps for consecutive processing cycles of the control system;and, c) repeats steps based on a refresh rate of the tracking system.26) A system according to any one of the claims 1 to 25, wherein therobot base includes a head mounted to a boom. 27) A system according toclaim 26, wherein the boom is attached to a vehicle. 28) A systemaccording to any one of the claims 1 to 26, wherein the system is usedfor at least one of: a) positioning objects or material in theenvironment; b) retrieving objects or material from the environment;and, c) modifying objects or material in the environment. 29) A systemaccording to any one of the claims 1 to 28, wherein the environment isat least one of: a) a building site; b) a construction site; and, c) avehicle. 30) A method for performing interactions within a physicalenvironment using a system including: a) a robot base that undergoesmovement relative to the environment; b) a robot arm mounted to therobot base, the robot arm including an end effector mounted thereon;and, c) a tracking system that measures a robot base position indicativeof a position of the robot base relative to the environment and whereinthe method includes, in a control system: i) acquiring an indication ofan end effector destination; ii) determining a robot base position usingsignals from the tracking system; iii) calculating an end effector pathextending to the end effector destination at least in part using therobot base position; iv) generating robot control signals based on theend effector path; v) applying the robot control signals to the robotarm to cause the end effector to be moved along the end effector pathtowards the destination; and, vi) repeating steps (ii) to (vi) to movethe end effector towards the end effector destination. 31) A methodaccording to claim 30, wherein the method is performed using the systemof any one of the claims 1 to
 29. 32) A computer program productincluding computer executable code, which when executed by a suitablyprogrammed control system causes the control system to control a systemfor performing interactions within a physical environment, the systemincluding: a) a robot base that undergoes movement relative to theenvironment; b) a robot arm mounted to the robot base, the robot armincluding an end effector mounted thereon; c) a tracking system thatmeasures a robot base position indicative of a position of the robotbase relative to the environment; and, d) a control system that: i)acquires an indication of an end effector destination; ii) determines arobot base position using signals from the tracking system; iii)calculates an end effector path extending to the end effectordestination at least in part using the robot base position; iv)generates robot control signals based on the end effector path; v)applies the robot control signals to the robot arm to cause the endeffector to be moved along the end effector path towards thedestination; and, vi) repeats steps (ii) to (vi) to move the endeffector towards the end effector destination. 33) A computer programproduct according to claim 32, wherein the computer program product isused to cause the control system to control a system of any one of theclaims 1 to 29.